EX LIBRIS.
Bertram C. 8L SEtntile,
3LIU3,, JB.Sc., ».*.®
WHEN Father Wasmahn's work Die Moderne Biologic
und die Entwicklungstheorie appeared in 1906 we wel-
comed it in this REVIEW and expressed the hope that "so
important and useful a book [might] shortly be translated
into English so as to be made available for those who do.
not read German." It is now 1910, and at last the desired
translation has appeared (Modern Biology and the Theory of
Evolution^ Translated from the Third German Edition by
A. M. Buchanan, M.A. London: Kegan Paul, Trench,
Trubner and Co, 1910. Price i6s.). As we dealt fully with
the book in its German dress it is not necessary to repeat
what has already appeared concerning it in these columns*
Suffice it to say that the translation appears to have been
adequately carried out and that the printer and publishers
have done their best to present the reading public with a
handsome volume. Let us be permitted to impress upon
those unacquainted with modern Biological work that in
the author of this book they have to deal not merely with
the ordinary type of Christian apologist, but with a man
who — as his most embittered opponents are constrained
to admit- — stands in the very front rank of biological
Workers, indeed, in his own particular line has no rivaL
Hence the only method of reply is that adopted by some
of his critics who suggest, or even openly state, that Was-
mann the Scientist suffers eclipse by Wasmann the Jesuit
where questions which may be supposed to affect religion
are under consideration* In a word the assertion is that
religious bias outweighs scientific accuracy* This curious
attitude is familiar enough in England, where the present
reviewer has not seldom heard books that at all diverged
from the fashionable scientific opinions of the moment
spoken of in slighting tones as "books written with &
bias against Darwinism "' or whatever other "ism *' may
have been in question. He once asked a person who had
made use of this criticism whether he had ever read a book
on Darwinism which was written with a strong bias in
favour of that system. The interlocutor was a man of scru-
pulous honesty, and, after reflecting for a moment, he re-
plied, "Do you know that never occurred to me before?"
In the same manner, Wasmann most properly replies
to his opponents:
I must acknowledge that with regard to the doctrine of creation,
the hypothesis of spontaneous generation and the application of the
theory of des.cent, I had a bias, and one that is directly opposed to
that of my reviewer. I had the intention of proving that a reason-
jible theory of evolution necessitates our assuming the existence
of a personal Creator, and I wished further to show that " spon-
taneous generation " was scientifically untenable, and, therefore,
could not be a postulate of science. Finally, I desired to prove that
to regard man from the purely zoological point of view is a one-
sided and mistaken proceeding. 1 was, however, forced to adopt
this threefold bias by the monists, who were exerting themselves
with a much greater bias to establish false philosophical postulates
in the name of biology, and to force them as " monistic dogmas "
upon all interested in science. I considered it my duty as a Chris-
tian and as a scientific man to protest vigorously against these at-
tempts at a fresh subjugation of the human intellect " (p. xxii).
It is much to be hoped that this book will have a large
Sale in this country, and certainly every Catholic school
and college which does not include it in its Library incurs
a grave responsibility. As our previous wishes with regard
to an English edition have borne fruit we will venture a
further aspiration, which is that before long this valuable
jvork may be available in a much cheaper form — -might we
dare even .to hope in the popular sixpenny form?
B.C.A.W.
MODEKN BIOLOGY
AND THE THEOKY OF EVOLUTION
Nihil Obstat
Sti. Ludovici, die 17 Aprilis, 1910
P, G. ROLWERK
Censor
Imprimatur
Sti. Ludovici, die 17 Aprilis, 1910
JOANNES J, GLENNON
Archiepus Sti. Ludovici
MODERN BIOLOGY
AND THE
THEOEY OF EVOLUTION
BY
EKICH WASMANN, S.J.
TRANSLATED FROM THE THIRD GERMAN EDITION
A. M. BUCHANAN, M.A.
LONDON
KEGAN PAUL, TEENCH, TEUBNEE & CO. LTD.
DRYDEN HOUSE, GERRARD STREET, W.
1910
Motto
Nulla unquatn inter fidem et ratio-
nem vera dissensio esse potest.
There can never be any real con-
tradiction between faith and reason.
(Constitutiones Concilii Vaticani, c.4,
De fide et ratione.)
Cum opus, cui titulus est : ' Biologie und Entwicklungstheorie,'
editio tertia, ab Erico Wasmann, Sacerdote Soc. Jesu, compositum aliqui
eiusdem Societatis revisores, quibus id commissum fuit, recognoverint
et in lucem edi posse probaverint, facultatem concedimus, ut typis
mandetur, si ita iis, ad quos pertinet, videbitur.
In quorum fidem has literas manu nostra subscriptas et sigillo
muneris nostri munitas dedimus.
Exaten, die 29 mensis Julii, 1906.
P. CAKOI/OS SCHAEFFEB, S.J.
Prov. Germ. Prsepositus.
( The rights of translation and of reproduction are reserved)
PREFACE TO THE SECOND
EDITION
AT the present day it is incumbent upon every educated man
to familiarise himself to some extent with the progress made
and the results attained by modern science, and especially by
biology. Only in this way will he be in a position to form
any opinion regarding the intellectual contest that rages
round certain important philosophical problems arising out
of biology, namely, the comparative psychology of man and
beasts and the theory of evolution. I have already dealt
with the former of these two problems in two special works,
intended for general reading, viz. : * Instinkt und Intelligenz
im Tierreich ' (' Instinct and Intelligence in the Animal King-
dom ') (third edition, Freiburg im Breisgau, 1905), and
' Vergleichende Studien liber das Seelenleben der Ameisen und
der hoheren Tiere ' (' Comparative Studies regarding the in-
telligence of ants and the higher animals ') (second edition,
Freiburg im Breisgau, 1900). My aim in the present work is
to comply with wishes expressed in various quarters, and to
render my articles on biology and evolution accessible to
readers in general.
These sketches appeared originally as a series of articles
in the magazine entitled Stimmen aus Maria-Loach, 1901-3.
Even in their present considerably expanded form they are
still sketches, with no pretensions to completeness,1 as they are
intended chiefly for readers who have no special knowledge
of the departments of science with which I have dealt. I hope,
1 The chapter on the relation between cellular division and the problems
of fertilisation and heredity has been rewritten. For much information
on the subject of botany I am deeply indebted to my colleague, Father J.
Rompel, S.J., Professor at the Stella Matutina Gymnasium at Feldkirch.
I have received very valuable suggestions from other specialists in various
branches of science, and I take this opportunity of expressing my gratitude
to them.
vi PKEFACE TO THE SECOND EDITION
however, that these dissertations will be of some use also to
students attending lectures on biology and the theory of
evolution ; they will find many facts presented to them from
a fresh point of view, and this is particularly true of the last
four sections on the modern theory of evolution. The chapter
headed ' Theory of Permanence or Theory of Descent ' is
based almost exclusively upon the results contained in my
previous 150 special articles on inquilines or guests among ants
and termites, and may be of interest to my colleagues who
have made a special study of zoology.
I trust that this work will be received in as friendly a
spirit as were the two previously mentioned psychological
works. In all three alike I have spoken as a Christian engaged
in scientific research, and I am firmly convinced that natural
•truth can never really contradict supernatural revelation,
because both proceed from one and the same source, viz. the
everlasting wisdom of God. Therefore the study of modern
biology and of the theory of descent, if carried on without
prejudice, can tend only to the glory of God.
THE AUTHOR.
LUXEMBURG,
Feast of St. Ignatius, 1904.
PREFACE TO THE THIRD
EDITION
THIS new edition contains many corrections and additions,
which our increased knowledge of this branch of science has
enabled me to make. The chapter on the physiology of
evolution and the section on the history of slavery amongst
ants are entirely new. The former throws some light on the
problem of determination, and the latter illustrates the
application of the theory of descent to the development of
instinct.
In its present form the book possesses more unity than it
did before. The two chief parts, those, namely, on cytology,
or the study of cells, and on the theory of evolution, are now
connected harmoniously with one another. The branch of
science with which I had to deal is, however, vast in itself,
and is being enriched almost daily by the publication of fresh
works, so that it is quite impossible to give an exhaustive
account of it in a limited space. Similar considerations led
even E. B. Wilson to have the new editions of his classical
work ' The Cell ' (1900 and 1902) reprinted without alteration,
and so I may, perhaps, be forgiven for having made only the
most absolutely necessary corrections and additions.
I wish to emphasise the fact that it is not my intention that
this work should serve as a complete textbook of the theory
of descent. The chapters on this subject are intended only,
on the one hand, to help the reader to form a clear conception
of the meaning of the theory of evolution, the philosophical
and scientific principles underlying it, and its limits and
causes ; and, on the other hand, to lay before him fresh evi-
dence, derived from my own special department of biology,
which tends to prove that the theory of evolution is really
better supported than that of permanence. This theory of
viii PEEFACE TO THE THIED EDITION
evolution, which I regard as a well-founded hypothesis, must
be polyphyletic and not monophyletic, if it is to correspond
with known facts.
With regard to the application of the theory of descent to
man, I abide by my previous opinion, and maintain that the
mental evolution of man from brutes is impossible, and that
his bodily descent from brute ancestors presents, from the
scientific standpoint, difficulties that have hitherto not been
solved.
In the chapter on the Division of Cells new diagrams have
been substituted for those which appeared in the earlier
editions, and in other places also fresh diagrams have been
added (fourteen in all), which are almost all original. Three
extra plates have been added, viz. Nos. II, VI, VII.
Since the appearance of the second edition it has been
translated into Italian by Era Agostino Dott. Gemelli, O.M.1
The worthy translator has inserted a long introduction in
which he states his own opinions on the theory of evolution,3
and throughout his translation he has inserted many remarks
of his own.3
The Italian edition, therefore, for which Gemelli alone is
responsible, is in many respects a totally new work, and I
trust that it will meet with as friendly a reception in Italy
as that accorded to the German edition on this side of the
Alps.
I am deeply grateful to all my colleagues who, by supplying
information or suggesting additions, have helped me in bring-
ing out this new German edition ; and I am especially indebted
to Father Eobert de Sinety for some valuable remarks on the
most recent discoveries regarding the problem of reduction
in Chapter VI. Father H. Muckermann, S. J., was kind enough
1 La biologia moderna e la teoria delf evohizione, Florence, 1906.
2 Gemelli does not call his theory the theory of evolution, but prefers to
speak of polyphyletic evolution (Polifilogenesi). As I also have expressed
myself in favour of polyphyletic evolution, there is no actual discrepancy
in our opinions, although I have retained the name ' theory of evolution.'
The chief difference between us and the Monists on the subject of evolution
is not so much whether it is polyphyletic or monophyletic, but it affects
rather the fundamental principles underlying it, for we accept the Christian
cosmogony, which is in direct opposition to that of Monism.
3 These remarks are in many cases added to my statements, in such a way
as to make it difficult to decide who is answerable for them. This remark,
however, does not apply to Chapter X.
PREFACE TO THE THIRD EDITION ix
to lend me the excellent photographs which are reproduced
on Plates VI and VII in this edition.1
THE AUTHOR.
LUXEMBURG,
Feast of St. Ignatius, 1906.
1 These and many other original photographs have been prepared by Dr.
Wm. Gray at the U. S. Army Medical Museum in Washington for his new
English textbook on physiology, that will shortly be published. (Cf. the
list of plates in this edition, p. xxxii.) Any other reproduction of Plates VI
and VII is forbidden.
A FEW WORDS TO MY CRITICS
THESE sketches on biology and the theory of evolution
appeared in book form barely two years ago, and I could
hardly expect that an edition of 2000 copies would be so
soon exhausted. My friends had in fact told me bluntly
that the book was too dry to find many readers, and that
it made too great demands upon the power of thought
possessed by our educated classes.
It is true that the book has not sold so quickly as Haeckel's
' Eiddle of the Universe,' but it is not a popular scientific
polemic aiming at the overthrow of Christianity, and there-
fore peculiarly welcome to those lower classes which are
especially interested in this overthrow. It is rather an attempt
at conciliation, based upon an objectively scientific foundation,
and it aims at harmonising the ideas of modern biology with
the Christian cosmogony, and thus it was not likely to prove
acceptable except to men of culture and intelligence. Never-
theless the comparatively quick sale of the book, and the
numerous discussions to which it has given rise, show that
it has awakened considerable interest among educated men
in Germany.1
The kind of interest thus awakened varies according to
the personal views of those in whom it exists. They may be
divided into three classes, viz. (1) supporters of Christianity,
(2) scientific specialists, and (3) opponents of Christianity.
The classification is not quite accurate, because there are
many scientific men, and especially many zoologists, among
the readers of the first class, and among those of the third
class zoologists form a considerable majority. Under the
second category I include those only who confine themselves
1 Germany is here used to include Austria and all countries where German
is spoken.
xi
xii A FEW WOEDS TO MY CEITICS
to considering the biological contents of my book, without
allowing their philosophical pre-suppositions to transpire.
Apart from some few expressions of opinion on points of minor
importance, the book has been very favourably received by
the supporters of Christianity in Germany, both Catholic and
Protestant. Some have even described it as a ' rescue from
bondage,' because it has shown the right tactics to adopt in
the struggle between Christianity and the monistic doctrine
of evolution. I will not allude further to the various reviews
of it that have appeared in the German Catholic papers. In
the Reformation of February 26, 1905, there is an article
entitled * Ein Jesuitenpater als Anhanger des Darwinismus ? '
(' A Jesuit as a supporter of Darwinism ? ') by E. Dennert, a
Protestant reviewer, well known as an opponent of Darwinism,
who expresses his complete agreement with my views on the
subject of evolution. Of the reviews by Catholic writers in
other countries, I will mention only three of the most important.
The first appeared in a North American periodical, The
Review, of November 24, 1904, and the reviewer's opinions
coincided on all points with my own. The second, which is
very thorough, appeared in the number for April and May
1905 of the Spanish Razon y Fe, and although the writer
at the close of his article says that he prefers for the present
to abide by the theory of permanence, still his verdict as to
the author's position with regard to the theory of evolution
is favourable. The third review, * L'Haeckelisme et les idees du
Pere Wasmann sur 1'evolution,' may be found in the Belgian
Revue des Questions scientifiques for \ January 1906. The
French critic, himself an eminent biologist, in the course of a
very careful article, shows that it is not possible to oppose the
monistic doctrine of evolution with success, unless we acknow-
ledge the claims of the scientific theory of evolution ; on this
point he agrees fully with the author's opinions.
Eeviews written by critics belonging to what I have called
the second class deal with the book from the scientific aspect.
On the whole they are appreciative and favourable, although
some few objections have been raised. I will mention only
the articles contributed by Professor Dr. C. Emery to the
BiologiscJies Zentralblatt (February 15, 1905) ; by Dr. E.
Hanstein to the Naturwissenschaftliche Rundschau (February
A FEW WORDS TO MY CRITICS xiii
2, 1905) ; by J. Weise to the Deutsche Entomologische Zeit-
schrift (1905, part I) ; by Dr. K. Holdhaus to the Verhand-
lungen der Zoologisch-botanischen Gesellschaft von Wien (1905,
parts 5 and 6) ; and by Professor H. J. Kolbe to the
Naturwissenschaftliche Wochenschrift (July 2, 1905).i
The critics of the third class are those who seek to maintain
their own monistic theory in opposition to the author, and
to prove his position as a Christian untenable. It was easy
to foresee that there would be many reviews written from this
standpoint, as unfortunately most of the zoologists of the
present day have monistic tendencies ; and the fact that my
book called forth such vigorous opposition may be regarded
as far more satisfactory evidence of its success than the most
appreciative comments proceeding from the Catholic party.
Why have the monists thought it necessary to pay so much
attention to my work ? The only psychological explanation
of their action is that they see in it a certain amount of danger
to the supremacy of their an ti- Christian views. For this
reason they do their best to draw as sharp a distinction as
possible between the author as scientist and as theologian.
They cannot help recognising the merits of the book, and
the only objections they can raise refer to minor points, or
are based on misunderstandings and misrepresentations, but
naturally they refuse to acknowledge that the author has
succeeded in reconciling biology in its recent developments
with the principles of Christianity, for such an acknowledge-
ment would at once deprive modern unbelief of one of its
chief weapons in the conflict with Christianity.
Of these hostile criticisms I can only refer here to the
most important, those, namely, of K. Escherich, H. von
Buttel-Reepen, Ernst Haeckel, August Forel, J. P. Lotsy
1 On pp. 426 and 427, where Kolbe has attempted to give a summary
of the ' results ' of my opinions, there are some misstatements, that are
probably due to some extent to Escherich's review, to which reference will be
made later. Kolbe's fourth point, that * polyphyletic origin of closely allied
forms is more likely than monophyletic,' is exactly the opposite of my
assertions. The remark on the sixth point regarding ' the great number of
primitive types ' is, to say the least, inaccurate. The statement on the ninth
point that the assumption of a ' creation ' of primary types is ' a dualism
irreconcilable with the principles of natural science ' is devoid of all proof.
The reviewer, however, seems to have had in his mind some notion of * creation
out of nothing,' because in discussing the tenth point he says emphatically
that ' nevertheless ' in another place I have assumed ' that the primary
types must originally have been formed out of matter.'
xiv A FEW WOEDS TO MY CRITICS
and F. von Wagner. They are not all written in the same
spirit, as the following examination of them will show.
' Kirchliche Abstammungslehre ' — the Church's teaching
on descent — is the title of a long article by Dr. K. Escherich,
lecturer on zoology, in the supplement to the Allge-
meine Zeitung of February 10 and 11, 1905. He speaks
very appreciatively of my position with regard to the
theory of evolution, and especially of the ninth chapter, in
which I have dealt with the inquilines or guests among ants
and termites from this point of view. But, on the other hand,
he believes that ' theological reasons ' have led me to assume
a polyphyletic evolution, which distinguishes as many ' natural
species ' as there are lines of evolution, independent of one
another, and he thinks that I have done this in order the
better to reconcile the doctrine of evolution with that of
creation. My opinions regarding the origin of life and the
creation of man seem to him inadmissible, for they contradict
the most important postulates of the monistic doctrine of
evolution. Escherich sums up the results, which he thinks
he can deduce from my opinions, and arranges them under
nine chief headings, whence he draws the conclusion ' that
any reconciliation of the doctrine of descent with ecclesiastical
dogmas is impossible.'
My reply to Escherich's review appeared in the supplement
to the Allgemeine Zeitung of March 9, 1905. In it I showed
that the reviewer's imaginary opposition between an eccle-
siastical and a non-ecclesiastical doctrine of descent indicated
a biased misrepresentation of facts. He ought to have
proved that the doctrine of evolution as a scientific hypothesis
and theory was incompatible with the Christian cosmogony,
but instead of doing so, he had recourse to the postulates of a
monistic philosophy, which are neither based on science nor
philosophically correct. I drew attention also to a number
of actual misunderstandings with regard to the * natural
species ' and the ' inner laws of evolution,' &c. These, I
believe, were accidental, but of the nine points which Escherich
ascribes to me as summing up my opinions, three at least were
wrongly so ascribed, and these were the very three which might
have been challenged from the scientific standpoint.
In the ' Closing Word ' appended to my reply by Escherich,
A FEW WORDS TO MY CRITICS xv
he acknowledged several of the misunderstandings as such,
but he adhered to his assertion that my doctrine of descent
ought to be described as ' illogical ' in contrast to the ' logical '
theory. Unhappily he forgot to add that the logical character
of the monistic view, which he maintains, has no scientific
basis, but rests upon the unproved postulates of a false philo-
sophy. He concluded by recommending my book to all
readers who had had a scientific education, but warned the
general public against reading it ! I am grateful to him for
this recommendation, as I wrote expressly for educated
people.
In the Archiv fur Rassen- und Gesellschaftsbiologie
(March- April, 1905) there appeared a very careful criticism
of my book, contributed by Dr. H. von Buttel-Eeepen, who
is a specialist on the subject of social insects. The review is,
on the whole, written in a friendly spirit, but it forces
into prominence the question of cosmogony. ' Where does
science end, and the Jesuit begin ? ' This is the subject for
discussion. The ' science ' which the book contains is praised
by von Buttel, but he prefers to have nothing to do with
' that web of inconsistency, which, solely in order to save a
number of dogmas, draws its illogical and untenable threads
over Wasmann's scientific work, obscuring the results of
research.' By this ' web of inconsistency ' he means my
views on the theory of creation, on spontaneous generation, and
on the descent of man. That in these points I have not been
' consistent ' in the reviewer's monistic sense, may soothe my
conscience, not only as a theologian, but also as a scientific
man and a philosopher.
By means of his lectures at the Berlin Singakademie
(April 1905), Professor Ernst Haeckel, the well-known prophet
of Darwinism, undoubtedly did very much to increase the
circulation of my ' Biology and the Theory of Evolution.'
Special importance may be attached to his criticism, as he
states expressly, both in the preface and in the supplement
to the printed edition of his lectures on the theory of evolution,
that he was induced to deliver them chiefly through the publica-
tion of my book. What was the result of this official criticism,
which Haeckel as the champion of German monism felt bound
/to pronounce ? On the one hand he welcomes my work as a
xvi A FEW WOEDS TO MY CKITICS
satisfactory proof that the Catholic Church has ceased to
oppose the doctrine of evolution, and on the other hand he
calls it a masterpiece of Jesuitical distortion and sophistry.
He bestows upon it the highest praise that could proceed
from his lips, when he says that the ninth chapter (The Theory
of Permanence or the Theory of Descent) might be incorporated
as a valuable addition in one of Darwin's works, but at the
same time he regards it as one of the achievements of ' the
marvellous system of falsification invented by the Jesuits.'
I cannot but be grateful to Haeckel for the contradictory elo-
quence with which he has denounced my book as a dangerous
* snare ' for all who are not yet perfectly convinced monists,
for I believe that his very denunciation has led no small number
of victims into that snare, and has induced them to read the
book which he has solemnly placed on the index for Monism.
It would be superfluous for me on this occasion to discuss
Haeckel's statements in detail. In an ' Open Letter to Professor
Haeckel,' which appeared on May 2, 1905 in the Germania and
in the Kolnische Zeitung, I answered his assertions clearly and
decisively.
' Wissenschaft oder Kohlerglaube ? ' (* Science or charcoal-
burner's Faith ? ') is the title of an article antagonistic to
me, that appeared in the Biologisches Zentralblatt for 1905,
Nos. 14 and 15. It was written by the well-known authority
on ants, Professor August Forel. He does not discuss ants
in this article, in which in fact he pays a high tribute to my
scientific knowledge, but he challenges my ' charcoal-burner's
faith/ by which he means my energetic defence of Christianity
against the attacks of Monism. Two years previously I
had contributed to the same paper (Nos. 16 and 17, 1903) a
calm and courteous criticism of Forel's monistic theory of
identity,1 and this was his reply to it, expressed however in
by no means the same appropriate terms, but in language
that showed irritability, occasionally bordering on fanaticism.
In the introduction to his article he states plainly why his
reply was so long delayed, and why it displays so much hostility;
he says : ' In the meantime Wasmann has worked out and
favoured us with a doctrine of descent sui generis. . . . Now
1 See my Instinkt und Intelligenz im Tierreich, Freiburg im Breisgau,
1905, 3rd edit., chap. xii.
A FEW WOKDS TO MY CKITICS xvii
that Wasmann is beginning to be the apostle of a new doctrine,1
I regard it as my duty to answer him.'
Forel was therefore annoyed by my attempt to show that
the theory of evolution was not irreconcilable with Christianity,
and instead of impartially disproving my opinions, he showed
a partisan spirit in trying to distort them, and allowed his
imagination free scope in ridiculing the * natural species,'
whose primitive forms I assumed to have been created by God.
His charges against ' charcoal-burner's faith,' or rather against
the Christian standpoint, are based upon a confusion of ideas,
such as one would hardly expect in a critic who has been ..
trained in philosophy. Finally, to crown his arguments, he *N
ingeniously makes fun of the letters S.J. (Societatis Jesu)
after my name ; he says S stands for scientist and J for Jesuit,
and advises me to put an end to the unhappy union of the
two letters. He goes even further and enlarges upon this
distinction in the following words : ' Wasmann S. is a scientific
man, whom I respect for his acumen and conscientious work ;
Wasmann J. is a scholastic Jesuit. But Wasmann S. is a slave
under the control of Wasmann J., and can be free and inde-
pendent only when he deals with matters on which he does not
come into conflict with Wasmann J. As soon as any dispute
arises, Wasmann S. ceases to think as a man of science and
Wasmann J. begins with his syllogisms and scholasticism
and all the war of words.'
Such an attack did not really require any answer at all,
as it revealed its character plainly enough. Nevertheless, I
wrote a short article in reply, entitled ' Wissenschaftliche
Beweisfiihrung oder Intoleranz ? ' (' Scientific Proof or In-
tolerance ? ') which appeared in No. 18 of the Biologisches
Zentraiblatt for 1905. I had no difficulty in showing that
it would have been better for Forel to have said nothing
than to have come forward with such weapons as the champion
of Monism.
In their attacks upon my book, both Haeckel and Forel
have had many followers in popular scientific circles of the
same tendency. There is nothing surprising in this fact,
and it does not call for any further comment.
1 These words allude to my lectures on evolution delivered in Germany
and Switzerland.
b
xviii A FEW WORDS TO MY CKITICS
It is more significant that Forel's joke about Wasmann S.
and Wasmann J. has been imitated even in highly learned
university lectures.1
Lotsy praises the author of ' Biology and the Theory of
Evolution ' very highly, and says : ' Wasmann is a Jesuit,
but at the same time he is one of the best zoologists of the
present day, and we must feel the deepest admiration for
his investigations into the life of ants. This very eminent
man writes on p. 271 : " Of two hypotheses in natural science
or natural philosophy, put forward as offering an explanation
of one and the same series of facts, it behoves us always to
choose the one which succeeds in explaining most by natural
causes, and on this principle we can hardly hesitate to choose
the theory of descent in preference to that of permanence."
But as soon as we have to consider man. . . .' Lotsy goes on
to refer to p. 283 of my book, where I have limited the scope
of zoology with regard to man to his body, declaring it and
its attendant sciences incompetent to deal with him on his
spiritual side. On this subject Lotsy remarks : * These
words remind me of Lamarck's saying, " Telles seraient les
reflexions que Ton pourrait faire, si 1'homme n'etait distingue
des animaux que par les caracteres de son organisation, et
si son origine n'etait pas differente de la leur." Are we to
accuse Wasmann of prevarication ? Certainly not. I fully
agree with what Forel said a few days ago in the Biologisches
Zentralblatt. Forel sees in Wasmann two distinct person-
alities, the scientist and the theologian, whom I shall designate
by A. and B.' Then follows verbatim Forel's distinction that
I have already quoted, the only difference being that for
Wasmann S. and Wasmann J., Lotsy writes A. and B.
Lotsy might easily have perceived the weakness of this
argument of Forel's, if he had really considered the passage
quoted from Lamarck, who agrees with me in declaring zoology
alone incompetent to deal with the question of the origin of
man. If Lotsy were consistent, he would have to see two
personalities, viz. a scientific man and a ' scholastic Jesuit,' in
Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck !
1 J. P. Lotsy, Vorlesungen uber Deszendenztheorien, mit besonderer Beriick-
sichtigung der botanischen Seite der Frage (' Lectures on theories of descent,
with especial reference to the botanical side of the question '), at the Imperial
University of Leiden, Part I, Jena, 1906, pp. 328, 329.
A FEW WORDS TO MY CRITICS xix
Special reference is due to a very detailed criticism of ray
book that appeared in the Zoologisches Zentralblatt, a
scientific periodical (1905, No. 22). The review was written
by F. von Wagner of Giessen, professor-extraordinary of
zoology, yet it is not of a purely scientific character, but
shows a partisan spirit, although the author's anti-Christian
bias is not so bluntly expressed as is the case in Haeckel's and
Forel's articles. It is, however, perceptible throughout the
review, which is consequently quite unlike the impartial
criticisms that we usually find in the Zoologisches Zentralblatt.
In the introduction to the nine pages in which he deals
with my book, von Wagner remarks that not a few of his
fellow-zoologists have been induced to believe that Wasmann's
attitude towards the theory of evolution indicates a ' change
of front on the part of the Catholic Church with regard to
modern biology.' The reviewer does his best to deliver his
colleagues from this * illusion,' and I am grateful to him for
doing so, as, like Haeckel and Forel, von Wagner does not
mean by ' modern biology ' merely its scientific results, but
also the monistic postulates which the opponents of Christianity
have insisted upon attaching to these results. I gladly agree
with the reviewer, and confess that my views do not coincide
with the postulates of a false philosophy, by no means free
from hypotheses. This is, however, all that he has really
succeeded in proving.
Von Wagner himself acknowledges that within my own
field of research I ' apply the principles of evolution in a
scientific spirit' (p. 691), and he describes my account of
modern cytology, or the study of cells, from the scientific
standpoint as 'very successful' (p. 693). He is, moreover,
particularly ' grateful ' for those parts of the book which
contain ' an excellent summary of the important results of
Wasmann's investigations from the standpoint of the
principle of descent/ The historical account, too, of the
development of biology ' describes it accurately in its general
outlines.'
We must now consider the reviewer's objections, which
can be summed up in one sentence (p. 692) : ' The book in
question has one author, but two editors, a scientific man
engaged in research work and a theologian. Consequently,
62
xx A FEW WOKDS TO MY CEITICS
the whole is a joint production ; the theologian takes the
lead, and the scientific man may assert himself only so far as
the former gives permission.' The conclusion derived by
von Wagner from this statement is that the book is written
with a bias from beginning to end.
The answer to this is obvious ; we need only apply the
just quoted words of the reviewer to his own review. * The
review in question has one author, but two editors, a scientific
man engaged in research work and a monistic philosopher.
Consequently, the whole is a joint production ; the monistic
philosopher takes the lead, and the scientific man may assert
himself only so far as the former gives permission.' The
conclusion that we derive from this statement is that the
review is written with a bias from beginning to end.
Let us now examine my book more closely and see how far
the ' bias ' imputed to it by the reviewers really exists, and
how far they are mistaken.
Even in my account of the historical development of
biology von Wagner discovers a bias, for he says that I have
singled out for praise none but Christian representatives of
this science. I do not understand why, if this were the case,
I spoke, as he says, with remarkably scant appreciation of
Cuvier's achievements in comparative anatomy, and men-
tioned Bichat's work in more eulogistic terms,1 whereas if
my opinion were really biased, I should have extolled Cuvier
rather than Bichat, as being an eminent Christian as well as a
scientific man. This fact shows that von Wagner's desire to
discover a particular bias in my work is the outcome of his
own imagination.
The bias of the book, as von Wagner has discovered (p. 694),
is revealed especially ' in what it does not contain.' The
author is accused of having purposely withheld from his readers
the more general biological evidence in favour of the theory
of evolution. I feel inclined to ask whether the reviewer has
really read the eighth and ninth chapters of his edition. I am
supposed not to have referred to Darwin, Lamarck and Geoffroy
St. Hilaire, whereas they are all mentioned on p. 169. He
seems not to have noticed the more general relations of the
1 In speaking thus I relied upon M. Duval's statements in his Precis
d'histologie, a book with which von Wagner seems not to be acquainted.
A FEW WOEDS TO MY CKITICS xxi
theory of evolution to the Copernican theory of the universe,
to modern geology and palaeontology (pp. 179-85), and the
long dissertation following them on the limits and causes of
the hypothetical phyletic evolution, but he notices my state-
ments regarding ' natural species ' and their connexion with
the theory of creation, for these statements give him another
opportunity of joining Escherich, Haeckel and Forel in imput-
ing to me a theological bias. On pp. 219, 220, I referred
expressly to the mass of indirect evidence supporting the
theory of evolution to be derived ' from comparative morpho-
logy, comparative history of evolution, comparative biology
and especially from palaeontology,' but I said that I had no
intention on this occasion of writing a textbook of the theory
of descent. 'Ko one could discover in this any intentional
concealment of evidence, who did not wilfully misinterpret
my words by imputing to them a bias that is not there. Such
a critic is plainly incapable of forming a just and objective
opinion.
Let us for a moment regard the matter from the point of
view of an extreme supporter of the theory of permanence.
He would have quite as much justification for discovering a
bias in favour of the theory of evolution from those very
statements and omissions, in which a fanatical advocate of
the theory discovers a bias hostile to it. He might, for in-
stance, try to account for the fact that I have not discussed
in detail the ordinary evidence in favour of the theory of
evolution, by declaring that this evidence has lost most of its
weight through Fleischmann's criticism, and therefore I have
been obliged to establish the scientific justification of the
evolution hypothesis upon the new and independent basis of
my own research. Moreover, when I have expressed my
preference for ' natural species ' rather than ' systematic
species,' he might discover an intention to set aside the theory
of permanence and replace it by that of evolution, under the
pretext that the latter is more easily reconciled with the
Christian doctrine of creation, &c. I maintain, therefore,
that, where it is possible to see in the same statements of any
author two totally opposite tendencies, it is plain that both
imputations are alike objectively without foundation. I
need say no more regarding von Wagner's method of treating
xxii A FEW WOBDS TO MY CBITICS
my book, as, whilst imputing a biased tendency to me, he
shows the same himself.
I must acknowledge that with regard to the doctrine of
creation, the hypothesis of spontaneous generation and the
implication of the theory of descent, I had a bias, and one
that is directly opposed to that of my reviewer. I had the
intention of proving that a reasonable theory of evolution
necessitates our assuming the existence of a personal Creator,
and 1 wrshed further to show that ' spontaneous generation *
was scientifically untenable, and, therefore, could not be a
postulate of science. Finally, I desired to prove that toregard
man from the purely zoological point of view is a one-sided and
1 was, however, forced to adopt this
threefold bias by the monists, who were exerting themselves
with a much greater bias to establish false philosophical
postulates in the name of biology, and to force them as 'monistic
dogmas ' upon all interested in science. I considered it my
duty as a Christian and as a scientific man to protest vigorously
against these attempts at a fresh subjugation of the human
intellect.
It is, moreover, psychologically very interesting to observe
how a reviewer, himself an ardent advocate of Monism, seeks
to discover throughout my book Christian tendencies, in order
to destroy as far as possible its scientific objectiveness. A
criticism undertaken on these lines cannot be truly free from
prejudice, and the absolutely biased character of von Wagner's
review appears most plainly in his closing words (p. 699) :
' There is always the same discord, when science is only on a
man's lips and not in his heart.' Because I do not accept the
unscientific postulates of Monism, all love of science is to be
denied me ! Is not that plainly monistic intolerance ? Accord-
ing to my opinion, science has its abode neither on the lips
nor in the heart, but in the intellect or, as von Wagner would
say, the brain, which he regards without doubt as the real
organ of thought in a human being.
And now I take leave of my critics,1 and commend the
present edition to their kind attention. In it, as far as lay in
1 A short reply to von Wagner's review has already appeared in Beispiele
rezenter Artenbildung bei Ameisengdsten und Termitengasten (written in
honour of J. Rosenthal, Leipzig, 1906, pp. 45-58 ; Biologisches Zentralblatt,
1906, Nos. 17 and 18, pp. 565-580), 55 (577) et seq.
A FEW WORDS TO MY CRITICS xxiii
my power, I have taken into account all the really well-founded
objections to statements in the previous editions, whether
these objections were raised by friends or by opponents. It is
in vain, however, to call upon me to conform to the tyrannical
requirements of Monism, and such a demand will remain
unsatisfied in the future, as it has done in the past.
CONTENTS
(^4 more detailed outline of contents is prefixed to each chapter)
PAGE
PREFACE TO THE SECOND EDITION ...... v
PREFACE TO THE THIRD EDITION _. . . . . . vii
A FEW WORDS TO MY CRITICS . . . ... . xi
CHAPTER I
MEANING AND FIRST DEVELOPMENT OF BIOLOGY
Introduction .......... 1
1. Meaning and subdivisions of Biology. Tree of the biological
sciences .......... 3
2. Earliest development of Biology. Aristotle. Albert the Great.
Roger Bacon ......... 8
3. Development of systematic zoology and botany. Linnaeus'
' System a naturae ' and modern syst atics . . . . 17
CHAPTER II
DEVELOPMENT OF MODERN MORPHOLOGY AND ITS BRANCHES
INVOLVING MICROSCOPICAL RESEARCH
1. Development of anatomy before the nineteenth century . . 25
2. Early history of cytology ....... 29
3. Methods of staining and cutting sections ..... 34
4. Use of the microscope in studying the anatomy and ontogeny
of Termitoxenia and other inquilines amongst ants and termites 37
5. Recent advance in microscopical research. Cytologists of
various nationalities ........ 45
CHAPTER III
MODERN DEVELOPMENT OF CYTOLOGY
1. The cell, a mass of protoplasm with one or more nuclei. Diver-
sity in shape and size of cells, and in number of nuclei . . 48
2. Structure of the cell examined more closely. Theories regarding
the structure of spongioplasm ...... 54
3. Minute structure of the nucleus. Chemical and physical
theories 60
4. Survey of the historical development of cytology ... 63
xxv
xxvi CONTENTS
CHAPTER IV
CELLULAR LIFE PAQE
1. The living organism as a cell or an aggregation of cells. Processes
of life involving movement ... ... 66
2. Activity of living protoplasm. Amoeboid movements of
Rhizopods and Leucocytes ... . 70
3. Exterior and interior products of the cell. Various biochemical
departments of work ....... 74
4. Predominance of the nucleus in the vital activities of the cell.
Vivisection of unicellular organisms ..... 77
CHAPTER V
THE LAWS OF CELL-DIVISION
1. Various kinds of division of the cell and nucleus. Direct and
indirect nuclear division ...... .85
2. Stages of indirect nuclear division (karyokinesis or mitosis) . 88
3. Survey of the process of karyokinesis. Centrosomes . . 97
CHAPTER VI
CELL-DIVISION IN ITS RELATION TO FERTILISATION AND HEREDITY
(Plates I and II)
Introductory remarks . . . . . . .104
1. The problems to be solved
2. Maturation-divisions of the germ-cells . ... 109
3. Normal process of fertilising an animal ovum . .119
4. Phenomena of superfecundation among animals, and double-
fertilisation in plants. Polyembryony . . . .127
5. Processes of conjugation in unicellular organisms and their
relation to the problem of fertilisation . . . . .130
6. Natural parthenogenesis . . . • . .135
7. Artificial parthenogenesis . . . . . . . 139
8. Fertilisation of non-nucleated egg-fragments (merogony) . 149
9. Review of the subject of fertilisation and conclusions. The
essential feature of fertilisation. Twofold purpose of fertilisa-
tion. Chromosomes as bearers of heredity. Mendel's Law.
Amphimixis. Interior laws of development governing organic
life ... 155
CHAPTER VII
THE CELL AND SPONTANEOUS GENERATION
1. The cell as the lowest unit in organic life. Are there any living
creatures whose organisation is more simple than that of the
cell ? The idea of individuality in unicellular and multi-
cellular organisms. All so-called ' lower elementary units ' in
the cell have no real existence . . . . . .179
2. Spontaneous generation of organisms. Untenable character
of the theories of spontaneous generation demonstrated by
modern biology. Theory of Creation a postulate of science . 193
CONTENTS xxvii
CHAPTER VIII
THE PROBLEM OF LIFE
PAGE
1. The problem of determination and its history . . . 209
2. More detailed discussion of the problem of determination . . 218
3. Embryological experiments on the eggs of various kinds of
animals .......... 228
4. Conclusions. Inadequacy of the Machine Theory. Vitalistic
solution of the Problem of Life ...... 235
CHAPTER IX
THOUGHTS ON EVOLUTION
1. Problem of phylogeny ....... 251
2. Four different meanings of the word ' Darwinism.' Critical
remarks upon them . . . . . . . 256
3. The subject of the theory of evolution as a scientific theory :
investigation of facts and causes with reference to series
of organic forms ........ 267
4. Theory of evolution considered in the light of the Copernican
theory of the universe. Biological evolution a natural con-
sequence of geological evolution ..... 272
5. Philosophical and scientific limitations of the theory of evolution.
First: Philosophical limitations. Recognition of a personal
Creator. His influence upon the origin of primitive organ-
isms. Creation of the human mind.
Second : Scientific limitations. Hypothesis and theory.
Monophyletic or polyphyletic evolution ? Problems still
to be solved regarding the course and causes of the hypo-
thetical evolution of a race ...... 279
6. Systematic and natural species. Importance of this distinction
from the point of view both of natural science and of philo-
sophy. Theory of evolution and the doctrine of Creation . 296
7. Summary of results ........ 302
CHAPTER X
THEORY OF PERMANENCE OR THEORY OF DESCENT ?
(Plates III— V)
1. Reasons for the fixity of systematic species .... 307
2. Direct evidence in support of the theory of evolution. Muta-
tion and cross-breeding as factors in forming species . . 312
3. Evolution of the forms of Dinarda. Conclusions drawn from it. 315
4. Indirect evidence in support of the theory of evolution derived
from the comparative morphology and biology of inquilines
amongst ants and termites ....... 327
5. Hypothetical phylogeny of the Lomechusa group. Origin of its
genera and species through the action of natural laws of
evolution ......... 330
6. Inquilines amongst the wandering ants. Their mimetic char-
acteristics. Comparison between Dorylinae inquilines of the
mimetic and of the offensive types, and the Atta inquilines . 340
xxviii CONTENTS
PAGE
7. Transformation of wandering ants' inquilines into termite-
inquilines. Recent confirmation and extension of this hypo-
thesis .......... 348
8. The family of Clavigeridae ; their characteristics prove, when
considered from the point of view of evolution, to be all due
to adaptation . . . . . .... 360
9. The hypothetical phylogeny of the Paussidae. Adaptation to
more complete guest-relationship has been the principle
controlling their evolution . . . . . . .364
10. The Termitoxeniidae, a family of Diptera. Their descent from
genuine Diptera may be proved from their adaptation char-
acteristics and the development of their thoracic appendages 379
11. The history of slavery amongst ants. Survey of the biological
facts upon which it is based. Conclusions .... 386
12. Conclusions and results. Theories of permanence and descent
compared with regard to their value in supplying explanations.
The latter alone can suggest natural causes to account for the
occurrence of beneficial adaptations, and therefore it reveals
the Creator's wisdom and power more strikingly than does
the theory of permanence ....... 425
CHAPTER XI
THE THEORY OF DESCENT IN ITS APPLICATION TO MAN
(Plates VI and VII)
Preliminary observations. Great importance of this question . 431
1. Is a purely zoological view of man justifiable ? Inadequacy
of such a view. What are we to understand by the creation
of man ? St. Augustine on this subject. Philosophical
reflexions on the creation of man. How far zoology is com-
petent to investigate the origin of man ..... 432
2. What actual evidence is there of the descent of man from
beasts ? 443
(a) A glance at the comparative morphology of man and
beasts. Wiedersheim's * testimony.' Skeletons of apes
and men. Rudimentary organs ..... 443
(6) The biogenetic law and its application to man. Haeckel's
progonotaxis of man. Criticism of the biogenetic law in
itself and in its application to man ..... 446
(c) The theory of direct relationship between man and the
higher apes. Their ' blood-relationship ' . 456
(d) Theory of remote community of origin between man
and apes. Palseontological arguments against this theory. 462
3. Criticism of recent palseontological and prehistoric evidence
for the descent of man from beasts .... 465
(a) Pithecanthropus erectus, a genuine ape .... 465
(b) The Neandertal man and his contemporaries. Schwalbe's
theory regarding Homo primigenius. Recent investigations
by Macnamara and Kramberger. Homo primigenius merely
an early species of man. Homo sapiens .... 467
(c) Conclusions. Haeckel's imaginary pedigree of the Primates.
Branco's opinion respecting the ' ancestors ' of man. A
glance into the future . . . . . . . 476
CONTENTS xxix
CHAPTER XII
CONCLUSION
PAGE
The rock of the Christian cosmogony amidst the waves of the
fluctuating systems evolved by human science. The storms at
the base of the rock 300 years ago, and at the present time.
The rock can never be overthrown by the tempests, because
no real contradiction between knowledge and faith can ever
exist 481
APPENDIX
(Plate VIII)
Lectures on the Theory of Evolution and Monism, delivered at
Innsbruck in October 1909 484
SUPPLEMENTARY NOTES . . . . . . .523
INDEX 525
LIST OF ILLUSTRATIONS
PIG. PAGE
1. Scheme for a series of sections of Termitoxenia (original) . 42
2. Cells of various shapes, occurring in Termitoxenia (original) . 50
3-6. Diagrams showing the historical development of our
knowledge of the structure of cells (after Schlater) . . 64
7. Experimental division of an Infusorian (Stentor) (after
Balbiani) <-„; . . 81
8. Direct nuclear division of the red blood-corpuscles (after Duval) 87
9-12, 13-16. Various stages of indirect nuclear division
(karyokinesis) (after Wilson) . . . .91 and 95
17-22. Diagrams of the maturation-divisions and formation of
polar bodies in the egg-cell (original) . . . .118
23. Transverse section of an embryo of Ascaris megalocephala
var. bivalens, at the blastula stage (original) . . 124
24-26. Pluteus larvae of Echinus and Sphaer echinus, and of their
hybrid (after Boveri from Korschelt and Heider) . . 151
27. Position of the spindles in an Ascaris egg (after Zur Strassen) 223
28. Position of the spindles in a very large Ascaris egg (after Zur
Strassen) 224
29. Dinarda Maerkeli Ksw. (original) ..... 316
30. Dinarda dentata Grav. (original) ..... 316
31. Dinarda Hagensi Wasm. (original) . . . . .316
32. Dinarda pygmaea Wasm. (original) . . . . .316
33. Lomechusa strumosa F. (original) . . . . . 331
34. Larva of Lomechusa strumosa (original) . . . .331
35. Atemeles pratensoides Wasm. being fed by Formica pratensis
Deg. (original photograph) . ... . . . 336
36. Mimeciton pulex Wasm. (original) . . . .341
37. Ecitophya simulans Wasm. (original) ..... 341
38. Xenocephalus limulus Wasm. (original) .... 344
39. Doryloxenus Lujae Wasm. (original) ..... 344
40. Doryloxenus transfuga Wasm. (original) .... 353
41. Discoxenus lepisma Wasm. (original) . . . . . 353
42. Termitodiscus Heimi Wasm. (original) . . . . 353
43. Pygostenus pubescens Wasm. (original) .... 357
44. Pygostenus termitophilus Wasm. (original) .... 357
45. Worker of Formica sanguinea Ltr. (original photograph) . 394
xxxii LIST OF ILLUSTKATIONS
PIG. PAGE
46. (a) Head of Formica sanguinea Ltr. ..... 398
(6) Head of Polyergus rufescens Ltr. (original photographs) . 398
47. Ergatoid queen of Polyergus rufescens Ltr. (original
photograph) 399
48. Worker of Polyergus rufescens Ltr. (original photograph) . 399
49. Worker of Strong ylognathus testaceus Schenk (original
photograph) ........ 403
50. Female of W heeleria Santschii For. (original photograph) . 406
51. Male of Anergates atratulus Schenk (original photograph) . 408
52. Cranium of the Neandertal man (after Schaafhausen) . . 468
53. Outline of the sagittal median curve :
I. Of the cranium of a modern Englishman
II. Of the cranium of a modern Australian black
III. Of the Neandertal cranium
IV. Of the Pithecanthropus cranium
V. Of the chimpanzee skull
(after Macnamara) .... . 469
54. Outline of the sagittal median curve :
I. Of a brachycephalic Lapp cranium
II. Of a dolichocephalic Australian cranium
III. Of the Neandertal cranium
(after Macnamara) ...... 469
LIST OF PLATES
At the End of the Book
PLATE PAGE
I. Diagrammatic representation of the process of fertilising
an egg-cell (after Boveri) (printed in colours)
To illustrate pp. 121-127
II. The Chromosome theory and Mendel's Laws (after Heider)
(printed in colours) . . . .To illustrate pp. 172, 173
III. Doryloxenus transfuga, Claviger testaceus, Pselaphus Heisei,
Paussiger limicornis and Miroclaviger cervicornis (from
original photographs) . . .To illustrate pp. 348-364
IV. Various species of Paussidae (from original photographs)
To illustrate pp. 364-379
V. Termitophile Diptera of the Family of T ermitoxeniidae
(from original photographs) To illustrate pp. 37-44 and 379-386
VI. (a) Skeleton of a man. (6) Skeleton of an ape (orang-
outang) (after original photographs by Dr. Wm. Gray,
see Preface, p. ix) . . .To illustrate pp. 445 and 462
VII. (a) Skull of a man. (b) Skull of an ape (orang-outang)
(after original photographs by Dr. Wm. Gray, see Preface,
p. ix) . . . . To illustrate pp. 445 and 462
VIII. Human skull found at le Moustier (after Hauser and
Klaatsch) To illustrate p. 511
MOBEEN BIOLOGY
AND
THE THEORY OF EVOLUTION
CHAPTER I
THE MEANING AND FIRST DEVELOPMENT OF BIOLOGY
' Knowledge is inexhaustible in its source, unlimited by time or space in its force, immeasurable
in its extent, endless in its task, unattainable in its aim.' — K. B. V. BAER.
1. MEANING AND SUBDIVISIONS OF BIOLOGY.
Biology in the wider and narrower signification (p. 3). Subdivisions of
Biology (p. 4). Tree of the biological sciences and its branches
(p. 5).
2. THE EARLIEST DEVELOPMENT OF BIOLOGY.
Aristotle as the father of the biological sciences (p. 9). Albert the
Great, the most prominent student of natural science in the
Middle Ages (p. 11). Roger Bacon (p. 16).
3. THE DEVELOPMENT OF SYSTEMATIC ZOOLOGY AND BOTANY.
Linnaeus' 'Systema naturae' the basis of modern systematic classifica-
tion (p. 18). The most recent works on systematic science (p. 21).
The place of systematics in biology (p. 24).
AT the close of any considerable epoch it is of peculiar
interest to look back upon the historical development of
nations and states during that period ; to compare their
position a century ago with that which they now occupy ;
to observe the rise and fall of their political power, and the
fluctuations in their political and intellectual importance
amidst the pressure of contemporary events, and to trace the
causes of these fluctuations. In the same way it is most
interesting at this juncture to look back at the development
of a science. The history of science is a branch of universal
history, not indeed accompanied by the thunder of cannon,
like the great battles of the world, but, in spite of its silent
working, it sometimes has more influence than war upon
the destiny of nations and of humanity as a whole.
2 MODEKN BIOLOGY
No one, I think, would deny that during the past century
the development of chemistry and physics, and of the technical
arts depending upon them, has been of the utmost importance
in advancing the growth of civilised nations, and so has played
no small part in the history of the world. Modern physics have
enabled men to avail themselves of the forces of fire and
water, and the discovery of steam power has altered the face
of the earth, for now it is covered with a network of railway
lines, upon which trains rush to and fro, whilst the sea too is
constantly traversed by sea monsters built of steel and driven
by steam, which bring the farthest ends of the world into
communication, and convey to still uncivilised nations the
achievements of modern progress. By means of physics, too,
has the human intellect succeeded in subjugating the mysterious
waves of ether, both visible and invisible, and now through
the electric light we have new suns ; electric telegraphs and
submarine cables have triumphed over the old limitations of
time and space, while Kontgen-rays penetrate even the human
body, and fix the outline of its skeleton on photographic plates.
The development of physics and chemistry has enabled men
to construct innumerable motors and machines, and to devise
chemical compounds used in various branches of industry,
resulting, on the one hand, in a complete revolution in the
economical conditions of the people, and, on the other hand,
supplying our armies with terrible guns and deadly explosives,
in the invention and perfection of which each nation strives
to outstrip its neighbours, in order to annihilate them more
speedily, should an opportunity occur.
It is obvious that astronomy and biology owe very much
to their kindred science — physics, and especially to optics
and mechanics, without which the extraordinary progress
made in recent times would have been impossible. Optics
and mechanics have supplied the astronomer and the biologist
with their instruments, and, in conjunction with chemistry,
have given them technical methods, bringing the infinitely dis-
tant near to the investigator's eye, enlarging the infinitely small,
and even rendering the invisible visible on the astronomer's
photographic plate and in the coloured sections of the micro-
scopist, revealing to the one the marvels of the heavens, and
to the other the secrets of the most diminutive living beings.
MEANING OF BIOLOGY 3
It is not, however, my intention now to dwell upon the
development of the physical sciences -and their influence in
changing the various circumstances of human life ; I purpose
to deal only with the development of biology, which cannot
boast of such wide-reaching triumphs. Nevertheless, the
history of biology in the nineteenth century forms part of the
history of the human intellect, and is an instructive piece of
what may be called internal history, of greater importance
to mankind than a merely superficial examination might lead
us to suppose.-
1. MEANING AND SUBDIVISIONS OF BIOLOGY
We must begin by clearly understanding what we mean
by biology. What is biology ? As the name tells us, it is the
science of life and of living creatures. This is biology in the
widest sense of the word, and it coincides with its oldest
historical signification, as it occurs in scholastic philosophy.
Biology, or the study of living creatures, is closely connected
with cosmology, or the study of the bodies composing the
universe, for, strictly speaking, the study of living creatures
includes the whole study of plants, animals and men, but this
is so vast a territory that we generally apply the name biology
to one comparatively small subdivision of it, and speak of the
biology of plants and animals in contradistinction to their
morphology, physiology, and morphogeny. Morphology deals
with the forms and component parts (organs, tissues, and
cells) of organisms. The history of individual development,
or Morphogeny, deals with the growth of the organic forms
from the egg to maturity. Physiology discusses the functions
of the various parts of the organism, and establishes their
relations to the process of life and also the chemical and
physical laws regulating their activity. Finally, Biology is
concerned with the external activities affecting the organisms
as individuals, and consequently governing their relation to
all other organic beings as well as to the inorganic world.
In this respect biology differs from Psychology, the proper
subjects of which are the processes of sensitive and intellectual
life — essentially internal activities, although these frequently
B 2
4 MODEKN BIOLOGY
come within the scope of biology in virtue of their outward
manifestations.
In the narrower sense of the word, therefore, biology may be
defined as the science dealing with the mode and relations of
life in animals and plants. Human biology forms a distinct
branch of knowledge, forming a part of anthropology, and is
no longer regarded as belonging to biology in the more restricted
sense of the word, now generally accepted by scientific writers.
With regard to the meaning of the word ' biology ' and the most
convenient definitions to be assigned to it, there are many different
opinions, only a few of which can be mentioned here briefly. Almost
all scientific men agree in retaining the old name ' biology ' (in the
Avider sense) to denote the whole mass of knowledge regarding
life and living creatures. 1 But there is great diversity of opinion
as to the designation of the special branch of that science, which
we have called oiology in the narrower sense. German zoologists
used to call it simply biology, until Ernst Haeckel suggested the
name (Ecology. (Ecology means ' study of dwelling ' or ' science
of keeping house/ it approaches the more restricted meaning of
biology, but does not cover it. This new name has found favour
not only with many zoologists, but also with botanists. Fr.
Delpino,'^ F. Ludwig,3 and J. Wiesner * speak of the phenomena
of plant life as the biology of plants, whereas other botanists, such
as K. v. Wettstein,5 prefer the name oecology of plants.
Fr. Dalil was the first German zoologist to suggest the adoption
of Ethology, or science of the habits of life, a word first introduced
by French scientific writers to replace biology in the narrower sense. 6
This new name would certainly be more applicable to animal
biology than Haeckel's oecology, but it is not applicable at all to
plants, as we can speak of ' habits of life ' only with reference to
creatures that possess instinct and psychological life. If we are
to have a new name, it ought to be applicable both to plants and
to animals with regard to their phenomena of life.
An eminent botanist, J. Keinke,7 is of opinion that we can
dispense with the word * biology ' in the narrower sense, and, in
order to avoid confusion when it is used in its wider sense, he
suggests the simple expression ' Mode of life among animals and
1 Cf. for instance, 0. Hertwig's Entwicklung der Biologic, im 19 Jahrhundert,
Jena, 1900.
2 Pensieri sulla Biologia vegetale, efcc., Nuovo Cimento, XXV, Pisa, 1867.
3 Lehrbuch der Biologic der Pflanzen, Stuttgart, 1895.
4 Biologic der Pflanzen, 1902, I.
5 Leitfaden der Botanik fur die oberen Klassen der Mittelschulen, 1901, 1.
6 Cf. Wasmann, ' Biologic oder Ethologie ? ' (Biolog. Zentralblatt, XXI, 1901,
No. 12, pp. 391-400).
1 'Was heisst Biologic ? ' (Natur und Schule, I, 1902, part 8, p. 449, &c.).
TEEE OF THE BIOLOGICAL SCIENCES 5
plants ' as a substitute for the word in its more restricted significa-
tion. This designation is clear and convenient enough, but I
scarcely think that it fulfils the requirements of science, for we need
some internationally intelligible word for ' mode of life ' or ' Lebens-
weise/ formed from Greek roots on the analogy of ' Morphology/
' Physiology/ &c.
To supply this deficiency the word bionomy or bionomics has been
introduced in England 1 and North America,^ and this is perhaps
the best word yet suggested to designate the mode of life of animals
and plants, for it denotes the laws governing life ' (/^os-vojuos),
and so means exactly what we defined as biology in the narrower
sense, and at the same time it avoids the ambiguity of the word
biology. I should have no objection to accept this new name
Bionomics, to designate the mode of life among animals and plants ;
but as it is not yet current in Germany, I may be permitted to
retain the old name.
The experimental study of the laws of heredity and variation has
recently been called Biometry. .3 In 1901 a new periodical appeared
in Cambridge (England) entitled Biometrica : A Journal for the
Statistical Study of Biological Problems. Biometry is, therefore,
synonymous with Statistical Biology.
The following simile may serve to illustrate more clearly
the original meaning of the word biology, and the various
modifications which it has undergone owing to the progress
made by science in the nineteenth century.
Biology, in its widest signification, embraces all that we
know about living creatures, and we may compare it with a
lofty tree having three main boughs, but many branches, and
its stem, boughs, and branches are the biological sciences. The
tree is crowned by twigs shooting from the main trunk, and
this crown represents the science dealing with man, or anthro-
pology, and the topmost of its twigs, rising up into the domain
of the intellectual sciences, is the psychology of man and
nations. Below it is human biology in the narrower sense,
then human physiology, human morphology and the history
of human development, all having many subordinate twigs,
1 Cf., e.g., G. K. Marshall and E. B. Poulton, ' Five Years' Observations
and Experiments on the Bionomics of South African Insects ' (Transactions of
the Entomological Society, London, 1902, part 3).
2 Cf. Ch. S. Minot, 'The Problem of Consciousness in its Biological
Aspects' (Proceedings of the American Association for the Advancement of
Science, XXXI, p. 272).
3 Cf . Chr. Schroder, 'Bine Sammlung von Ref eraten iiber neuere biometrische
Arbeiten' (A Ilgemeine, Zeitschrift fur Entomologie, IX, 1904, Nos. 11 and 12,
]> 228, &c.).
6 MODEKN BIOLOGY
bearing, for the most part, the same names as the correspond-
ing ramifications of the zoological stem. Some few branches
belonging to the crown have names of their own, to which
zoology supplies analogies only ; such are ethnology and
archeology, psychopathology, and medicine.
Below the crown a great bough springs from the main
trunk of the biological sciences : this is zoology. Its chief
offshoots are animal psychology and animal biology (animal
bionomics) and the physiology, morphology, and morphogeny
of animals. In the course of the nineteenth century a great
number of little twigs grew out of each of these branches, of
which only a few can be mentioned here. Out of animal
biology or bionomics sprang trophology, or the science dealing
with the food of animals ; oecology, or the science dealing with
their habitations ; animal geography, dealing with their
distribution ; and, further, their parasites have been studied,
and the tendency of certain animals to live with other animals
or near to some particular plants (symbiosis). This has given
rise to investigations of a biological nature into the way of life
of ants and termites, and one of the most fertile offshoots of
modern biology is the study of the inquilines among ants and
termites. We cannot do more than name nervous physiology
which, with its offshoots, cerebral physiology, physiology of
the external organs of sense and of the nerve tracks, threatens
to take the place of animal psychology, now said to be out
of date.1
Modern morphology has even more ramifications, branch-
ing out in one direction into systematics, or the science of
systematic classification, and in the other into morphology
proper, which latter is subdivided into exterior and interior
morphology, the interior comprising topographical anatomy,
histology or study of the tissues, and cytology or study of
the cells — all three well-developed offshoots of morphology.
Moreover, all these branches of morphology have their counter-
parts on the physiological side, in the physiology of the organs,
tissues, and cells.
Morphogeny, or the history of the development of animals,
1 On this subject cf. my article ' Nervenphysiologie und Tierpsychologic '
(Biolog. Zentralblatt, XXI, 1901, No. 1, pp. 23-32) and also Instinkt und
Intelligenz im Tierreich, 1905, chap. ii.
TEEE OF THE BIOLOGICAL SCIENCES 7
has two great branches, viz. ontogeny, or the history of
individual growth, and phylogeny, or the history of the race
development. Ontogeny is divided into embryology and post-
embryonic development, which includes the phenomena of
metamorphosis, metagenesis, &c. Finally we must allude to
animal pathology as a branch of zoology. Reference has
already been made to animal geography as a branch of animal
bionomics.
Nearer the root of the tree springs the lowest bough of
biology, viz. botany. Nothing is found on it corresponding
to the most dignified offshoot of the zoological bough — animal
psychology, because plants have no consciousness, and even
the most sensitive of them show only a faint resemblance to
conscious life.1
There are, however, on the botanical bough a good many off-
shoots corresponding to the other parts of zoology ; we have the
biology (bionomics) of plants, which includes plant-geography,
and we have also plant-physiology and morphology, plant-
anatomy and cytology, and finally phytopathology.3 The
botanical branch is further distinguished by possessing one
suspiciously luxuriant and poisonous looking offshoot, which
boldly rises up to the branch of the crown that we have called
' medicine,' and this is bacteriology. Fortunately it has a
less poisonous side in the phenomena of fermentation and
assimilation of nitrogen, which are in many respects beneficial
to man.
To our astonishment we see that our tree bears one or two
apparently dead branches of considerable size ; they spring
from the same point of the main trunk as the zoological and
botanical boughs respectively, and they are called palceozoology
and palceophytology. They are, however, by no means really
dead, although they deal with the extinct ancestors of the
animal and vegetable kingdoms of the present day.
In the main trunk supporting the crown and the branches
1 Many modem botanists regard this analogy as constituting real identity
(homology), but they are certainly mistaken. Cf. for instance, Haberlandt,
Die Sinnesorgane im Pflanzenreich zur Perzeption mechanischer Reize, Leipzig,
1900. For a criticism on these views, see J. Reinke, Philosophic der Botanik,
1905, 66, &c., 83, &c.
'z The distinction between anatomy and histology is less marked in the
case of plants, as their tissues do not differentiate themselves so sharply
into organs as do those of animals.
8 MODEEN BIOLOGY
of the tree of biological knowledge with all their offshoots and
twigs rises a stream of sap, representing the comparative and
generalising elements belonging to all the biological sciences ;
these connect all the parts of the tree with one another and
enable us to view them intelligently as a whole, and at the
same time they enlighten us as to its growth. Comparative
psychology effects a close connexion between the zoological
branch and the crown of the tree ; comparative biology and
physiology, comparative morphology, anatomy and histology,
comparative cytology and comparative morphogeny send
streams of life through all the branches and twigs of the great
tree, and show that they are all living parts of one vast whole.
Chemistry and physics, too, and especially mechanics of
organic structures, are represented in the roots of the tree, as
biochemistry and biophysics, and they connect it with the
surrounding domain of the inorganic sciences. But the
quintessence of all the sap flowing in the tree of biological
knowledge is the scientific conception of life, and the trunk of
the tree, which supports and nourishes all these branches and
twigs, is the science of life.
2. THE EARLIEST DEVELOPMENT OF BIOLOGY
We have just seen how the tree of biological sciences grew
rapidly in the nineteenth century, and produced an indescrib-
able abundance of offshoots, leaves, blossoms and fruit on
branches previously bare. Let us now consider the origin of
this tree and how it fared whilst still an insignificant seedling.
It was not planted first in the year 1800, nor did it suddenly
develop on New Year's Day, 1801, into a trunk sturdy enough
to support all the branches and twigs which the new century
was destined to add to it. It is far older than this, and we
can trace its history for several thousand years. The seed,
whence this tree has grown, was planted when God breathed
into the first man the breath of life, as we read in the beautiful
figurative language of Holy Scripture. The breath of God's
spirit, dwelling in man, its all-embracing power of understanding
and its never satisfied thirst for knowledge, form the hidden
motive power, the inner living force of this tree. Man has
always been possessed by a thirst for knowledge, both among
EARLY BIOLOGISTS 9
civilised nations and among the wild children of nature. The
Eskimo of the present day adorns the walrus ivory implements
used in shooting his arrows with dogs' heads and outlines of
reindeer, birds and human beings, showing that the shapes of
the living creatures around him have deeply impressed them-
selves upon his mind ; and, in the same way, the cave-dwellers
of Central Europe scratched rough sketches of fish, horses and
other animals on reindeer bones. Even if the famous repre-
sentation of a long-haired mammoth with a long mane, which
was found on a piece of a mammoth's tooth, proves not to be
genuine, and the much finer engraving, on a reindeer antler
from the cavern at Kessler, of a reindeer grazing, is in all
probability a modern forgery, still, as J. Ranke says,1 it is
difficult to say exactly when the germ of biological research
latent in the mind of man first assumed a scientific form, and
appeared as a young plant above the ground. We know,
however, one famous gardener, who tended the little tree
most skilfully, and that is Aristotle the Stagirite.
Aristotle had predecessors, no doubt ; the animal system
devised by the followers of Hippocrates of Cos had already
prepared the way for him,2 yet he certainly deserves to be
called the Father of Biological Science. His classical works
' Historia animalium,' * De partibus animalium,' and * De
generatione animalium ' are the foundations of our scientific
systematic classification and biology, of morphology, anatomy,
and morphogeny.3 In his writings he actually mentions 500
kinds of animals.4 As he does not allude to many other
varieties that are very common and occurred in ancient Greece
in his day, we must assume that he did not think it necessary
to speak of all the animals with which he was familiar. He
divides animals into two chief classes, Zvaifta or with blood
(more correctly red-blooded), and avaifia or bloodless, and
1 Der Mensch, II,. Leipzig and Vienna, 1894, 459, &c.
2 Cf . R. Burckhardt, ' Das koische Tiersystem, eine Vorstuf e der Zoologischen
Systematik der Aristoteles ' (reprinted from the Verhandl. der naturf. Gesell-
schaft in Basel, XV, 1902, part 3, pp. 377-414).
3 R. Burckhardt, ' Das erste Buch der aristotelischen Tiergeschichte ' (Zoo-
logische Annalen, I, Wiirzburg, 1904, part 1). Also ' Zur Geschichte der biolo-
gischen Systematik ' ( VerJiandlungen der Naturf. Gesellschajt in Basel, XVI,
1903, 388-440).
4 We cannot here discuss their division into different classes. Gunther
remarks that the number of varieties of fish known to Aristotle seems to
have been 115 (Handbuch der Ichthyologie, 1886, p. 3).
10 MODEEN BIOLOGY
this division practically answers to the modern classification
into vertebrates and invertebrates. The eight yevrj /^ejccrra,
or chief classes of the Aristotelian system, agree roughly with
our chief classes in the animal kingdom. The conception of
the eZSo? or species, introduced by Aristotle, underlies our
modern conception of it. But the great philosopher was not
only a pioneer in systematic classification, he was equally
eminent as a morphologist, an anatomist, a biologist, and an
embryologist. He compared animals with regard to their
form and structure, and studied their mode of life and the
history of their development.
How great a biologist Aristotle was is proved by the fact
that some of his discoveries were rediscovered in the nineteenth
century, and were regarded as brand-new triumphs of modern
science. Aristotle knew that many sharks do not only produce
their young alive, but that in their case the young before their
birth are nourished by a process closely resembling that of
mammals (development of a placenta). This fact was re-
discovered by Johannes Miiller, a famous anatomist and
zoologist (1801-58). Moreover, Aristotle was aware of the
difference between male and female cephalopods, and had
observed that young cuttlefish possess a vitelline sac near the
mouth. The accuracy of these old observations has been
completely proved by modern research. Bretzl has thrown an
astonishing light upon the extent and importance of the
botanical knowledge possessed by Greeks of Aristotle's time.1
When we consider the well-merited prestige enjoyed by
Aristotle as founder of biology, when we remember the enor-
mous wealth of knowledge, interspersed though it be with many
errors, contained in his works, we cease to wonder that for two
thousand years everyone, who studied biology at all, studied
Aristotle almost exclusively, quoted Aristotle, made extracts
from Aristotle, and wrote commentaries on Aristotle. The
work of the Younger Pliny in this department is insignificant
in comparison with that of his great predecessor, and even
in some respects shows a falling off. Pliny, however, has been
the chief source of information for most of the students of
nature both of antiquity and of the Middle Ages, who derived
1 Die bolanischen Forschungen des Alexanderzuges, Leipzig, 1903. Cf.
the review in the Botanisches Zentralblatt, XCIII, 1903, p. 97, &c.
EAKLY BIOLOGISTS 11
from him their biological knowledge, and adopted as genuine
all the stories found in Pliny's * History of Animals,' without
in any way testing their truth. A standard work of this
description is the famous ' Physiologus ' or ' Bestiarium,' in
which all the legends connected with zoology are collected,
with edifying morals appended to them.
It would he unfair not to acknowledge that, among the
great scholastic philosophers of the thirteenth century, there
were a number of men who did their best to carry on inde-
pendent scientific research. Besides St. Thomas Aquinas,
the Dominican Order produced in that century three great
men, conspicuous not so much for their scholasticism, as for
their proficiency in another department of knowledge.
These were Thomas of Chantimpre, Vincent of Beauvais, and
Albertus Magnus or Albert the Great (1193-1280),1 of whose
treatise upon animals Victor Carus says, in his ' Geschichte der
Zoologie,' p. 226, that, in comparison with the works of the
two previously mentioned writers, it is far more thorough
and composed with greater self-confidence.
Thomas of Chantimpre was a pupil of Albertus Magnus,3
and that Vincent of Beauvais used his books is proved by
his numerous quotations from them. Although, like all his
predecessors, Albert the Great based his work on Aristotle,
1 Cf. F. A. Pouchet, Histoire des Sciences naturelles au moyen-age, ou Albert
le Grand et son epoque consider cs comme point de depart de Vecole experimentale,
Paris, 1853. Cf. also Fr. Ehrle, S.J., ' Der selige Albert der Grosse,' in
Stimmen aus Maria-Laach, XIX, 1880 ; G. v. Hertling, Albertus Magnus,
Beitrdge zu seiner Wilrdigung, written in honour of the 600th anniversary of
his death, Cologne, 1880; E. Michael, S.J., Geschichte des deutschen Volkes
vom 13 Jahrhundert bis zum Ausgang des Mittelalters, III, 1903, pp. 445-460 ;
Arthur Schneider, Die Psychologie Albert des Grossen : Nach den Quellen
dargestellt, I, 1903, Vorwort VIII.
2 He describes himself as an auditor eius per multum tempus. (Thomas
Cantipratanus, Bonum universale, Duaci, 1627, 1. 2, c. 57, § 50, p. 576. Cf.
E. Michael, S.J., ' Albert der Grosse,' in the Zeitschrift fur Katholische Theo-
logie, 1901, part 1, p. 43.) Borman is therefore probably mistaken in thinking
that Thomas of Chantimpre's work was one of Albert the Great's chief sources
of information in the compilation of his book on animals. V. Carus falls
into the same mistake in his Geschichte der Zoologie, p. 227. Cf. also Alex.
Kaufmann, Thomas von Chantimpre, Cologne, 1899. Thomas was a canon
regular in the Augustinian monastery at Chantimpre before he entered the
Dominican Order in 1232. His book, entitled Liber de rerum natura, was
subsequently translated into German by Konrad Megenberg, who belonged
to the cathedral chapter at Ratisbon. Its German title is Buch der Natur
(Book of Nature), and it records the results of much independent research.
The same author's work on bees (Bonum universale de apibus] is a pious
picture of manners rather than a treatise on natural history.
12 MODEEN BIOLOGY
he took more pains than any of them to make independent
observations of his own. His treatise on animals consists of
twenty-six books, of which nineteen correspond to the writings
of Aristotle, whilst seven are of independent origin.1
Book XX, the first of those containing his own results,
deals with the nature of animals' bodies in general, and Book
XXI with the degrees of perfection attained by them
(de gradibus perfectorum et imperfectorum animalium), a quite
modern idea in classification, on the lines of comparative
morphology of animals. The remaining five books deal with
animals singly, arranged alphabetically within the larger
groups. These seven books show conclusively that the author
was not content to write a commentary on Aristotle, but
aimed at rendering his work more complete by adding the
results of his own investigations.
Albert the Great's seven books * De vegetabilibus et plantis,'
which contain his views on botany, have been carefully studied
and justly appreciated by E. Meyer, in his * Geschichte der
Botanik,' IV, Konigsberg, 1857, but the more important
work on zoology has hitherto met with far too slight recog-
nition among scientific men. An attempt to display its
merits, made by Karl Jessen in 1867, was frustrated, owing
to the defective state of most editions of Albert the Great's
works.3
E. von Martens subsequently published some observations
on several of the mammals mentioned by him, and Victor Carus
has devoted a few pages to Albert the Great in his ' Geschichte
der Zoologie,' but without discussing his work in detail.3
Although Carus is by no means a partisan of the Church, he
feels bound to confess, on p. 224, that ' Albert, to whom the
cognomen " Great " may justly be conceded, is undoubtedly
the chief writer of the thirteenth century on the subject of
natural science.' If Carus had adhered to the principle which
he himself laid down, and had foreborne to judge Albert the
Great as a zoologist by the standard of a modern writer on
1 In the complete edition of Albert the Great's works, published in Paris
by Vives, the treatise on animals is contained in vol. xi (De animalibus pars
prior) and vol. xii (De animalibus pars altera).
2 ' Alberti magni historia animalium ' (Archiv fur Naturgeschichte,
XXXIII, vol. i, 1867, pp. 95-105).
3 Munich, 1872, pp. 224-237.
EARLY BIOLOGISTS 13
science, he would probably have spoken in more favourable
terms of his achievements in zoology.
Although Albert the Great could not completely disentangle
himself as a zoologist from the prejudices and fancies of his
predecessors, his merit lies, not merely in his having gone
back from Pliny to Aristotle, but also in his having led the
way to independent research, which does not rely blindly
upon authority, but looks for itself.1
R. Hertwig is perfectly correct in stating in the most
recent edition (seventh) of his * Lehrbuch der Zoologie ' (1905,
p. 7) that Albert the Great even began to collect his own
zoological observations. In many passages of his work on
animals he refers to his own investigations, and, when he
describes anything, he frequently adds a remark to the effect
that he has himself seen the thing in question, and even possesses
it in his collection. He devotes several chapters to the habits
of falcons, which he seems to have studied with particular
interest. In one place he tells us that he took a short sea
voyage for zoological purposes, and on the shore of an island
he collected ten or eleven kinds of * bloodless sea-beasts.'
After recording the various tales told about the propagation
of fish, he adds : ' I believe that none of all this is true, for
I have myself made diligent investigations, and have questioned
the oldest fishermen engaged in salt and fresh water fishing,'
and he proceeds to give the results of his observations and
inquiries. He declares that by personal observation he has
disproved the popular theory that the left legs of a badger
1 Men such as Albert the Great are enough to refute the discovery made
by certain followers of Darwin, that Christianity has ' stifled the spirit of
scientific research ' and has ' caused a kind of hostility to the idea of busying
the mind with natural objects.' It is unfortunate that such prejudiced
statements have found their way into even our modern text-books of zoology.
See, for instance, R. Hertwig, Lehrbuch der Zoologie, 1900, p. 7. The following
words, which I quote from Hertwig, cannot be applicable to Albert the Great :
' The question how many teeth a horse has was discussed in many contro-
versial treatises, in which the authors used all the heavy artillery at their
disposal, but it did not occur to one of the learned men to look inside a horse's
mouth and see for himself.' It is to the credit of the author of the above-
mentioned excellent text-book of zoology, that the words just quoted have
been omitted in the two last editions of his book (1903 and 1905). It is
satisfactory to observe that the achievements of mediaeval scholars in the
domain of natural science are gradually receiving fairer treatment, and are
being judged by a more unprejudiced standard. Cf. also J. Norrenberg,
* Der naturwissenschaftliche Unterricht in den Klosterschulen ' (Scientific
Instruction in Monastic Schools), in Natur und Schule, III, 1904, part 4,
pp. 161-169.
14 MODERN BIOLOGY
are shorter than the right legs, -and he relegates the stories of
geese growing on trees, and other zoological marvels, into their
proper sphere as fictions of the imagination.1 It is true that
his statements are interspersed with a good many mistakes.
He is right in saying that flies have two wings, but wrong in
giving them eight legs — and his famous pupil, Thomas Aquinas,
is falsely accused of having reckoned ants among the reptilia
quadrupedia, and thus of having fallen into an opposite error.3
It is hardly necessary to point out how impossible it was for
him to correct the old legends with reference to exotic animals,
and so he says that the porcupine shoots its quills at its enemies,
that the wild unicorn grows tame when caressed by a maiden,
&c. We ought to bear in mind that to a German student
of nature in the thirteenth century no other source of informa-
tion about foreign animals was accessible than the old fabulous
stories. What pains Albert the Great took to obtain trust-
worthy information about animals that he had never seen,
is proved by his admirable account of the methods then in use
in the whalefishery.
Careful studies in another quarter have recently shown
that Albert the Great followed an independent method of
investigation. Dr. E. Hertwig, Professor of Zoology at the
University of Munich, suggested to Dr. H. Stadler to make a
critical examination of Albert's zoology and botany. The
full result of this examination has just been published in the
Forschungen zur Geschiclite Baierns, XIV, 1906, first and second
parts, pp. 95-114, but Stadler communicated a good deal of
it previously, at a lecture delivered on March 20, 1905, to the
* Verein fur Naturkunde ' in Munich. The title of the lecture
was : ' Albert the Great as an independent student ' ; I
•subjoin some extracts from it : —
This very prolific writer was a scholastic, but lie occupies a
position on a level with Aristotle rather than subordinate to him,
1 The story of the geese growing on trees probably originated in the fact
that the barnacle goose (Lepas anatifera) often attaches itself to floating
tree trunks.
2 In the Summa Theologiae, I, q. 72, ad 2. In Vives' edition (1871) the
passage reads as follows : ' Per reptilia vero (intelleguntur) animalia, quae
vel non habent pedes . . . vel habent breves, quibus parum elevantur ut
lacertae et tortucae.' There is a note on the word tortucae : ' Sic codices,
Bed nescio qua incuria in Parmensi et in omnibus editionibus formicae.' Tortuca
is tartaruga, tortue, tortoise, and is rightly reckoned among the reptiles,
only a constantly repeated misprint has turned tortoises into ants !
EAKLY BIOLOGISTS 15
and did not simply reproduce Aristotle's statements, but, as far
as he could, explained, completed and expanded them. He dis-
played great shrewdness and keen intelligence in carrying on his
favourite observations on the animals and plants of Germany,
whence he derived the evidence for his scientific statements that
he based upon Aristotle. His writings therefore contain all the
information on natural history possessed by the people of Germany
in his day ; he describes the life of animals as observed by intelligent
huntsmen and farmers, fishermen and bird-catchers ; everywhere the
biological element and his own personality are prominent, and
for this reason his writings form a sharp contrast to the dry
book-learning of the periods preceding and following his lifetime.
It is true that in dealing with botany he follows the lines of the
pseudo- Aristotelian work ' De plantis/ really written by Nicholas
Damascenus, but under the form of excursus he gives a far better
account of the subject, based upon his own observations. He
describes very correctly the vascular bundles of the plantain leaf and
the medullary rays of the vine, and divides plants into two classes,
cortical and tunical, a division approximately corresponding to
that of monocotyledonous and dicotyledonous. He distinguishes
parenchyma and bast-fibres in the large stinging nettle, hemp
and flax ; he knows the difference between the inner and outer
bark, and the importance of each to the life of a plant. He has
observed the square stem of the deadnettle, and the diversity in
growth between plants in isolation and when cramped for space.
He describes very clearly the difference between a thorn and a
sting ; he attempts a classification of leaves according to the
shape, notices that plants with woody stems have bud-scales,
and herbaceous plants have naked buds, and he recognises, as a
peculiarity of the grape vine, the fact that fruit and tendrils are
opposite to the foliage leaves.
In speaking of blossoms he draws attention to their various
forms of insertion, and mentions stamens, pistil and pollen, although
he confuses the pollen with wax. He comments upon the deciduous
calyx of the poppy, tries in a very primitive fashion to classify
the forms of the corolla, insists upon the importance of the seed
in preserving the species, and gives a very fair classification of
fruits. The position and the significance of the ovules and of
the tissues connected with nutrition did not escape his notice.
The sixth book, * De vegetabilibus/ contains many admirable
descriptions of single plants, especially of the mistletoe, the hazel,
the alder, the ash, the date-palm, the poppy, borage and rose, and
in the case of the last-mentioned he gives an excellent account
of the aestivation of the calyx and of the alternation of the parts
of the flower, and suggests the true explanation of their significance.
We may speak in similar terms of his work on zoology, for
which, however, we are unfortunately obliged to use the very
unsatisfactory edition published by Auguste Borgnet in Paris, 1891,
16 MODEEN BIOLOGY
so that much in it appears open to question. Of animals known
in Germany, Albert begins by describing the German marmot and
the earless marmot, the two kinds of marten, the garden dormouse
and the common dormouse, and he is the first writer who alludes
to the chamois, the badger, the rat, the ermine and the polecat.!
He gives charming accounts of the mole, the marmot and the
squirrel ; he knows the Lepus variabilis of the North and the polar
bear ; he describes a whaling expedition and remarks that in his
day the elk, the bison, and the aurochs were to be found only in
the extreme east of Germany. His description of the cat displays
great sympathy with animals and very sharp powers of observation.
In dealing with birds, he discusses the various falcons in the
greatest detail, but he is well acquainted with the other birds of
prey. He speaks of the peculiar structure and purpose of the
woodpecker's claws, and considers the distribution of the hooded
crow and the habits of migratory birds.
Blackcock, grouse, and heathcock were familiar to him, and
he knew many kinds of singing birds (four varieties of finches,
two of sparrows and three of swallows), also the nutcracker and
kingfisher ; he describes the nest of the magpie and the habits of
the cuckoo with great accuracy. The lecturer proposed to speak
of Albert the Great's knowledge of fishes on another occasion ;
he stated that Albert had dissected insects and had perhaps recog-
nised the digestive system and heart. He gives a correct account
of the development of cockchafers and wasps, and also of caterpillars
and their spinning process, and of the habits of the ant-lion. Of
other creatures, the best description given as the result of his own
observation is perhaps that of the jelly-fish.
Among the learned Franciscans of the thirteenth century,
Eoger Bacon, the doctor mirabilis, deserves special mention,2
as he is in many respects the equal of the great Dominican,
Albertus Magnus. His chief services to science are in the
domain of physics, chemistry and medicine, rather than in
that of the descriptive natural sciences. Considering the age
in which he lived, he had wonderfully advanced opinions
regarding physiology. Much attention has been paid to Bacon
by Emile Charles,3 who declares that the results stated in his
1 In the printed text of the lecture there is a query after the word
rat, but having had some correspondence with Stadler, I infer from a letter
dated December 4, 1905, that the query ought to be omitted, as Albert the
Great was really the first to describe the rat.
2 See Dr. H. Felder, 0. Cap. Geschichte der wissenschaftlichen Studien
im Franziskanerorden bis um die Mitte des 13 Jahrhunderts, Freiburg i. B.,
1904, pp. 379-402.
3 Roger Bacon, sa vie, ses outrages, ses doctrines d'apres des textes inedites,
Paris, 1861.
DEVELOPMENT OF BIOLOGY 17
work ' De vegetabilibus ' surpass those of Albert the Great. We
receive an impression of something quite modern, in fact
almost anti-vitalistic, when the mediaeval Franciscan speaks
thus of the relation in which chemistry (which he calls alchimia
speculative!,) stands to the other natural sciences : l
Because students are not acquainted with this science, they
also know nothing of its bearing upon natural history, for instance,
the origin of living creatures, plants, animals and men. . . . For
the constitution of the bodies of men, animals and plants depends
upon an intermingling of elements and fluids, and proceeds in
accordance with laws similar to those governing inanimate bodies.
Consequently whoever is ignorant of chemistry, cannot possibly
understand the other natural sciences, nor theoretical and practical
medicine. .
3. THE DEVELOPMENT OF SYSTEMATIC ZOOLOGY AND BIOLOGY
As soon as the age of discoveries began in modern times,
much more interest was taken in the study of nature, and the
tree of biological knowledge put forth one branch after another,
all of which were full of vigorous life. In our historical sketch
we must follow this process of division, and we will begin by
considering the growth of systematic classification, leaving
for the present the development of some other branches.2
It was natural that external differences in form should be
the first things to attract the attention of a student, in the
case both of plants and of animals ; later on he tried to learn
something about the mysteries of their constituents, of their
configuration, and of the vital phenomena of living organisms.
It was natural, therefore, for systematic zoology and that
scientia amabilis, systematic botany, to develop earlier than
the other branches of biology. We cannot do more than
mention the chief pioneers in systematics. Edward Wotton,
an Englishman, wrote in 1552 a book called ' De differentiis
1 Opus tertium, c. 12, ed. Brewer, 39 : Et quia haec scientia ignoratur
a vulgo studentium, necesse est ut ignorent omnia quae sequuntur de rebus
naturalibus ; scilicet de gencratione animatorura, et vegetabilium et animalium
et hominum : quia ignoratis prioribus necesse est ignorari quae posteriora sunt.
Generatio enim hominum et brutorum et vegetabilium est ex elementis et
humoribus et communicat cum generatione rerum inanimatarum. Unde
propter ignorantiam istius scientiae non potest sciri naturalis philosophia
vulgata nee speculativa medicina nee per consequens practica. . . .
2 Cf. R. Burckhardt, ' Zur Geschichte der biologischen Systematik,' Bale,
1903 (Verhandlungen der Naturf. Gesellschaft in Basel, XVI).
18 MODEKN BIOLOGY
animalium,' in which he returned to Aristotle's system, which
he developed by adding to it the group of zoophytes. Another
Englishman, John Kay (1628-1705), l denned the Aristotelian
idea of species more clearly. His works, ' Methodus plantarum
nova' (1682) and 'Historia plantarum' (1686-1704), are very
important in systematic botany, whilst his synopses of various
classes of animals, especially of quadrupeds and snakes (1693),
mark an epoch in systematic zoology. In this way Kay, the
son of an English blacksmith, facilitated the work done by the
great Swedish knight Karl v. Linne (Linna3us), who was born
in 1707, being the son of a Protestant pastor in Rdshult. A
year after the birth of Linna3us died his chief forerunner in
botanical research, the eminent Frenchman, Joseph Pitton de
Tournefort (1656-1708), who in his ' Elements de botanique
ou methode pour connaitre les plantes ' laid the foundation of
our present classification of plants.
The work of Linnaeus (1707-78) marks a fresh stage in
the growth of the tree of biological knowledge, and caused it
to become a vigorous trunk with many branches. Under his
influence it grew strong enough to support the wealth of
offshoots which were destined to spring from it during the
nineteenth century. He made many journeys to Central
Europe in order to study the chief collections of his day, and
with unflagging industry he acquired the material for his
great work, the ' Systema naturae,' which stands alone of its
kind and is of the utmost importance in the history of biology.
The first edition appeared in 1735, the fifteenth (which was
the last revised by Linnaeus himself) in 1766-8. The most
complete and best known is the seventeenth edition of the
1 Animal Kingdom ' brought out by Gmelin, 1788-92.
The chief value of the ' Systema naturae ' lies not so much in
the fact that Linnaeus has in it formed systematic groups of
all previously described varieties of animals and plants, adding
many fresh ones to those already known, but rather in his
having introduced in his binary nomenclature a fixed scientific
terminology, so that exact statements of laconic brevity
thenceforth took the place of long-winded descriptions. This
work of Linnaeus had as important a bearing upon the develop-
ment of descriptive natural science, as the introduction of a
1 Ray died on January 17, 1705, not, as is generally stated, in 1704.
SYSTEMATIC CLASSIFICATION 19
written language has upon the development of a nation. Until
a language possesses a grammar and a vocabulary, it is only
a scientific embryo ; its elements lack sharpness and clearness ;
it has, so to say, no framework to which they can be attached
in orderly fashion.
There is no need for a long explanation of the binary
nomenclature. It is enough to say briefly that to every
species of animal and plant a scientific double name is assigned,
consisting of a generic and a specific name, both latinised
in form, and as these names are constant, universally current
and unchanging, they are free from arbitrary fluctuations in
use, such as are of common occurrence in the case of popular
names. To the generic name, which is a noun, the differentia
specified is added by connecting with it the specific name, which
is an adjective. Canis familiaris, Carabus auratus, and Carabus
nitens may be taken as typical examples. Whoever gives a
name of this kind adds a concise description of the animal to
serve as a means of identifying its species, and a writer using
the name appends to it in abbreviated form that of the author
who first gave it and described the animal in question,
so that, when in future any one reads Carabus auratus, L.
(Linnaeus), he knows exactly once for all what form it is
intended to designate. In this way a name such as Carabus
auratus, L., becomes a generally recognised scientific appellation,
leaving nothing to be desired in the way of clearness and
simplicity. Through the use of the binary nomenclature,
the whole zoological and botanical system has been reduced
to a classified catalogue, well arranged and visible at a glance,
and in devising it Linnaeus conferred an inestimable boon
upon biology. The inspiration thus in so simple a manner
to arrange logically the vast multiplicity of forms in the animal
and vegetable kingdoms is like Columbus' egg — before Linnaeus
appeared, no one knew how it could be made to stand at all,
but after Linnaeus had once for all set it upright, no one had
anything to do but to follow his example.
On account of his ' Systema naturae ' Linnaeus is to
be reckoned as the founder of modern systematic science.
His system of nomenclature is still the standard one, and will
probably continue to be so. The laws of zoological nomencla-
ture, as elaborated at the close of the nineteenth century by a
c2
20 MODEKN BIOLOGY
committee, specially appointed for the purpose at recent
zoological congresses,1 and universally adopted in scientific
circles, are only a logical carrying out and detailed specialisa-
tion of the principles laid down by Linnaeus. At the annual
meeting of the German Zoological Society in 1891, it was
decided to appoint a committee to lay down rules securing
uniformity in zoological nomenclature.3 In order to have a
firm basis on which to decide disputed points of priority, the
German Zoological Society caused a reprint of the tenth
edition of Linnaeus' ' Systema naturae ' to be issued, thus marking
the year 1758, in which the tenth edition first appeared, as the
date when systematic zoology originated, and fixing as the
standard generic names those used at that time by Linnaeus.
The International Botanical Association is now dealing
with the question of botanical nomenclature at the Inter-
national Botanical Congresses, of which the first was held in
Paris in 1900, and the second at Vienna in 1905.
Linnaeus' ' Systema naturae ' is a monumental work, such as
could be accomplished only at one period, at least by a single
individual. By means of the further development of systematic
zoology and botany, effected by a closer study of European
fauna and flora, as well as by the exploration of foreign coun-
tries, which has supplied a boundless and ever-increasing
wealth of material, systematic science has now attained
such gigantic proportions, that no single human intellect, not
even the genius of an Aristotle, would be capable of grasping
and assimilating it in all its details. In the year 1901 the
total number of species of animals known to science amounted
to at least 500,000, of which more than half are insects. In
giving the number of species of beetle at 100,000 we are probably
rather understating it. In the vegetable kingdom it is
estimated that there are about 200,000 species scientifically
described, divided into 11,000 genera — there are 50,000
species of cryptogams alone.
1 Regies de la Nomenclature des ttres organises, adoptees par les Congres
Internationaux de Zoologie, Paris, 1889 et Moskou, 1892 (Paris, 1895);
Report on rules of Zoological Nomenclature, to be submitted to the fourth
International Congress at Cambridge by the International Commission for
Zoological Nomenclature (Leipzig, 1898) ; Regies de la Nomenclature Zoologique
adoptees par le cinquieme Congres International de Zoologie (Berlin, 1901).
2 Verhandlungen der Deutschen Zoolog. Oesellschaft, 1891, p. 47 ; 1892,
p. 13 ; 1893, p. 89, &e.
SYSTEMATIC CLASSIFICATION 21
In order to collect the enormous mass of information on
systematic zoology which is now scattered in numberless
articles in numberless scientific periodicals and books,
the German Zoological Society determined, at their first
general assembly in 1891, to issue a great systematic work
entitled 'Species animalium recentium' or 'Das Tierreich'
(' The Animal Kingdom '), which should contain systematically
arranged descriptions of all the existent kinds of animals as far as
they are at present known. This great plan, which in Linnaeus'
time was not beyond the power of one man, can now only be
carried out by a scientific society having at its disposal many
workers and abundant means ; and even so it is doubtful
whether the new ' Animal Kingdom ' will be completed by the
year 2000. I have made a careful calculation with regard
to entomological literature, the results of which will perhaps
be of interest here.1
Every number of the work is to be arranged according to
the same detailed plan, therefore, from the nineteen numbers
that had appeared in 1894, we can form some idea of the
probable extent of the whole.3 Assuming that the same
method is followed in subsequent numbers as in those that
have already appeared, for the Order of Coleoptera alone,
according to a moderate estimate, 111 volumes of 500 pages
each will be required, for the whole class of insects at least 300
volumes of 500 pages, and for the whole animal kingdom at
least 500 volumes of 500 pages. These 500 volumes would
contain approximately 15,625 signatures, so that if the work
is to be completed in 100 years, 156 must be issued yearly.
But, as a matter of fact, since 1897 on an average less than
fifty signatures have appeared each year.
It is not my wish to take a pessimistic view of the matter,
but to give the reader some idea of the advance made in
biological knowledge. Let us hope, therefore, that the whole
enormous task will be completed within a reasonable period,
before the ' Twilight of the Gods ' foretold by Wala sets in, for
1 Cf . my discussion of the first numbers of the ' Tierreich ' in Natur und
Offenbarung, XLIII (1897), 508 ; XLIV (1898), 635.
2 Cf. the annual reports submitted to the meetings of the German Zoological
Society by Professor F. E. Schulze, the general editor. The publication of the
work has now been undertaken by the Berlin Academy of Science. By
the summer of 1905 twenty- three numbers had appeared.
22 MODEKN BIOLOGY
this would probably be a twilight of zoologists also ; let us
hope that the zoology of the future will derive much pleasure
and satisfaction from this creation of the German Zoological
Society ; in any case, the calculation I have made will serve
to give my readers some approximate conception of the enor-
mous strides made by systematic zoology in the course of the
nineteenth century.
Modern botanists, too, have undertaken the publication
of vast systematic works, continuing the enormous task of
systematisation on Linna3us' principles. One of these works
is ' Die natiirlichen Pflanzenf amilien nebst ihren Gattungen und
wichtigeren Arten,' von A. Engler und K. Prantl (' The natural
families of plants together with their genera and more im-
portant species,' by A. Engler and K. Prantl). The Phanero-
gams were completed before the end of the nineteenth century,
in a space of about twenty years, and are contained in eleven
stately volumes, but the Cryptogams are not finished yet.
Another huge work on botany, the counterpart of the
* Species animalium recentium,' is being brought out by A. Engler
for the Eoyal Academy of Science in Berlin, under the title
' Eegni vegetabilis conspectus.' It has been 'appearing at
intervals since 1900, and numerous collaborators in all parts of
the world are engaged on it. We may trust that there are fewer
hindrances in the way of its completion than in that of the
' Tierreich,' in the case of which the enormous class of insects
presents great difficulties, though it is to be hoped that these
will eventually be overcome.
There is one respect, however, in which the systematic
advance of modern zoology and botany is not on the lines
of Linna3us' ' Systema naturae.' Linnaeus was unable to
avoid using external differences as the distinctive marks of his
systematic groups, and in this way he was led to unite in an
artificial system forms that bore no natural relationship to
one another. In describing and classifying plants and animals
modern systematic science can avail itself of the assistance
of other biological sciences, especially of anatomy and of
morphogeny, or the history of individual development, and
thus it attains to a more or less successful natural classifica-
tion of organic forms. In spite of this difference, however,
it is true that modern systematic science is based upon
SYSTEMATIC CLASSIFICATION 23
Linnaeus and his ' Systema naturae,' for without this achieve-
ment of his powerful intellect we should at the present time
have had no natural systems of plants and animals.
The fact that the German Zoological Society regarded it as
necessary to issue a fresh edition of Linnaeus' ' Systema natura'e,'
and to undertake the publication of a great work on systematic
zoology on the same lines, is testimony enough to the import-
ance of systematics or the science of classification in the develop-
ment of biological knowledge. It shows at the same time how
deeply indebted the representatives of modern science are to
Linnaeus, and it is to be regretted that in some of the more
recent books on zoology Linnaeus is mentioned as the founder
of the ' unintelligent zoology of species,' and this in more or
less plain language.1
To a certain class of Haeckelists, systematic science seems
like an inconvenient old man, who threatens to check them
in their bold intellectual tricks and fantastic speculations,
precisely because the actual multitude of forms in the animal
world does not coincide with their ideas, and because they are
too impatient to be willing to master the subject-matter of
1 R. Hertwig is however justified in stating in his Lehrbuch der Zoologie,
7th edit., 1905, p. 9, that post-Linnsean zoologists, and especially entomologists,
have made it their sole aim to describe the greatest possible number of new
species, making quantity rather than quality the measure of their achievements.
Unfortunately, even at the present day this class of pseudo-systematic
biologists is not quite extinct, and there are still some who flood the scientific
periodicals with superficial or even ' provisional ' descriptions, and thereby
put obstacles in the way of studying some groups of animals, for other, more
thorough workers, who can make nothing of these superficial descriptions,
are hindered by being obliged by the law of priority to take them
all into account. An almost incredible story is told of a l scientific
worker ' who was employed about fifty years ago at a great museum, and was
paid £1 for each new genus and Is. for each new species that he established.
In order to work more quickly, he had two bags beside him, one filled with
Greek and the other with Latin names. If he wanted a name for a
new genus, he put his hand into the Greek bag and pulled out a name hap-
hazard, and bestowed it upon his genus. If, on the other hand, he wanted
a name for a new species, he had recourse to the Latin bag, and labelled it
with the first adjective that he caught up. It can easily be imagined how
applicable the new names thus assigned were to the genera and species, and
the descriptions which he appended as ' original ' to these names were equally
suitable. Such work as this was really ' unintelligent zoology of species,'
but it would be unfair to regard zoology of species as responsible for such lack
of intelligence. There are excrescences in every branch of knowledge, and
they do not occur more frequently in the systematic zoology of the Linnaean
school than in the modern doctrine of evolution. Ernst Haeckel's famous
book, The Riddle of the Universe, affords a striking instance of unintelligent
blunders on the part of the Darwinian supporters of this doctrine. See my
criticism of the same in Stimmen aus Maria- Loach, LX, 1901, p. 428, &o.
24 MODEKN BIOLOGY
systematics before beginning their speculations. They com-
pletely forget that but for this stern old father they would
have no existence at all.
Mere systematics is certainly by no means the ideal of bio-
logical knowledge ; it is not an end in itself, but is only an
indispensable aid to biological research. It bears the same
relation to the other biological sciences as the dry heart-wood
of a tree bears to its tissues permeated by life-giving sap ; it
forms the skeleton or scaffolding for other sciences. But just
as in the human body the eye has no right to reproach the
bones of the foot for not responding to the vibrations of ether,
so modern morphology and morphogeny ought not to look
down upon systematics for not perceiving many things that
these branches of science can discover. In science, as in the
living organism, the principle of the subdivision of labour
holds good, and the greater the perfection attained by any
science, and the more numerous its departments, the more
indispensable is it to distinguish clearly the subject-matter
with which each single subdivision deals, if any solid progress
is to be made.
Let us apply this consideration, the truth of which no
modern scientific man will question, to Linnaeus' position
with regard to biology. Scientific- classification or systematics
was his speciality, and it was a boon to science that Linnaeus
with his vast intellect devoted himself to it rather than to
anatomy and physiology, for the formation of a strong
systematic science was the first and most necessary starting
point for all the other branches of biological science, if they
were to thrive at all. Without it zoology and botany would
have remained a hopeless chaos of forms, through which no one
could have found his way.
In order to produce a g*eat systematic work like Linnaeus'
' Systema naturae,' even at that time a man was required who
should devote his whole ability to this end, for otherwise it
would have been unattainable. When his pygmy successors,
who have inherited the achievements of his genius, reproach the
great Linnaeus with being merely a one-sided systematist, they
show themselves to be both short-sighted and ungrateful.
CHAPTEK II
THE DEVELOPMENT ON MODERN MORPHOLOGY AND ITS
BRANCHES INVOLVING MICROSCOPICAL RESEARCH
1. THE DEVELOPMENT OF ANATOMY BEFORE THE NINETEENTH CENTURY.
Malpighi and Swammerdam's anatomy of insects (p. 26). Bichat's
Comparative Anatomy (p. 26). G. Cuvier's services to the various
branches of zoology (p. 27).
2. EARLY HISTORY OF CYTOLOGY.
The invention of the microscope (p. 29). The discovery of the cell and
nucleus (p. 30). Schwann and Schleiden's theory of cells and its
subsequent development (p. 32). The meaning of protoplasm (p. 33).
3. METHODS OF STAINING AND CUTTING SECTIONS.
General and particular methods for definite microscopical purposes (p. 34).
4. USE OF THE MICROSCOPE IN STUDYING THE ANATOMY AND DEVELOPMENT
OF A DIMINUTIVE FLY (Termitoxenia) (p. 37);
and in investigating genuine inquiline relationship in the case of guests
among ants and termites (p. 44).
5. RECENT ADVANCE IN MICROSCOPICAL RESEARCH.
Cytologists of various nationalities (/>. 45).
1. THE DEVELOPMENT OF ANATOMY BEFORE THE
NINETEENTH CENTURY
WE have already shown how Aristotle may justly be regarded
as the founder of modern systematics,1 and he may with equal
right be called the first morphologist in the modern sense,
because he carried on a comparative study of the varieties of
form among animals. Aristotle laid the foundation of the
science of morphology in his work 'De partibus animaliurn,' and
Galen (131-201 A.D.) continued what Aristotle had begun, for
his famous work on human anatomy is based chiefly upon post-
mortem investigations on the higher animals, and so should be
called animal rather than human anatomy. The real originator
of human anatomy was Vesalius (1514-64), who dissected
human bodies, and thus was able to correct many errors arising
out of Galen's studies of animals.
1 Cf. also on this subject Professor R. Burckhardt, 'Zur Geschichte der
biologischen Systematik ' (reprinted from the Verhandlungen der Naturf. Gesell-
schaft in Basel, XVI, 1903, pp. 388-440).
25
26 MODEKN BIOLOGY
Marco Aurelio Severino (1580-1656), a Calabrian, was the
author of the first book on general anatomy. It was published
in Nuremberg in 1645, and bears the title : ' Zootomia Demo-
critaea, id est anatome generalis totius animalium opificii libris
quinque distincta.' Severino treats the ' lower animals ' in a
very curt fashion ; they fare better at the hands of writers
towards the close of the seventeenth century. Marcello
Malpighi, a Bolognese physician (1628-94), wrote a ' Dis-
sertatio epistolica de bombyce ' (1669) on the anatomy of the
silkworm, and this work opened the way to the anatomical
study of insects, for the discovery of the Malpighian tubes,
of the heart, nervous system, tracheae, &c., for the first time
revealed insects as organic masterpieces, whose wonderful
construction is scarcely inferior in perfection to that of the
higher animals, and is more worthy of admiration, because
of its diminutive size.
Johann Swammerdam (1637-85), who lived at Amsterdam,
in his ' Bijbel der natuure' (Biblia naturae), published 1737-8,
describes with astonishing accuracy the internal structure of
bees, ephemera, snails, &c. ; and whoever is acquainted with
the excellent anatomical discussion of the larva of the goat-
moth, published in 1760 by Pieter Lyonet of Maastricht,
cannot fail to recognise its merits even at the present time,
when we can avail ourselves of greatly improved instruments
and technical methods in dealing with the same subject.
The great scientists mentioned ' above inaugurated a new
era in anatomical knowledge, yet morphology was still not a
systematically organised science, but only a collection of
interesting monographs. It was raised to the rank of a special
science at the beginning of the nineteenth century, by Bichat,
a Frenchman, who introduced the idea of systems of organs
and systems of tissues. Bichat's ' Traite des membres en general '
(1800) and his ' Anatomie generale' (1801) created comparative
anatomy, for he divided the constituent parts of the bodies
of animals into organs and tissues, and into systems of organs
and tissues, thus fixing a firm basis for the comparison of the
constituent parts of various animals. It is true that this idea
of Bichat's was not altogether new ; Aristotle, Galen, and
Albert the Great distinguished heterogeneous and homogeneous
parts among the constituents of the bodies of animals. The
EAKLY ANATOMISTS 27
heterogeneous parts are the individual organs, the homo-
geneous are the tissues, which may be found in various organs,
and of which the organs are composed.
A famous Italian anatomist, Gabriele Antonio Fallopius
(1523-62), as early as the sixteenth century wrote ' Tract at us
quinque de parti bus similibus,' in which he distinguished and
described a considerable number of tissues. In 1767 Bordeu,
a Frenchman, devoted an entire work to one kind of tissue,
viz. the mucous connective tissue; his book bears the title
' Eecherches sur le tissu muqueux ou organe cellulaire.' Still
it was Bichat who first arranged the homogeneous tissues as a
scientific whole, distinguishing them from organs and systems
of organs. A system of organs is a complex of organs working
together to discharge the same vital function and so forming
one physiological whole. A system of tissues is a complex of
tissues consisting of the same morphological elements, and so
forming one logical whole, from the point of view of compara-
tive morphology. Two examples will explain this distinction.
The digestive system in man is a system of organs, for it is
made up of several organs which unite to produce one and
the same physiological result, though they are formed of
various kinds of tissue ; for, in addition to epithelial tissue,
both connective and muscular tissues enter into their structure. •
But the glandular system in man is a system of tissues, for it
consists of essentially similar tissues, viz. modifications of the
epithelium, which serve very various physiological purposes ;
such are the gland of the intestine, the renal gland, the salivary
gland, the sweat gland, &c. In other cases the distinction
between a system of organs and a system of tissues is not so
strongly marked as in those to which I have just referred.
For instance, when we speak of the nervous system of man,
we are alluding to both a system of organs and a system of
tissues. Nevertheless, in theory the two systems are totally
distinct even here.1
A far greater man, and one who had much more influence
on the development of comparative morphology, was Georges
Cuvier (1769-1832). He was born at Mompelgard and educated
1 Textbooks on zoology treat chiefly of systems of organs, and those on
histology chiefly of systems of tissues, therefore a writer on zoology is apt
to ignore the histological point of view, and vice versa, which is disastrous
to perspicuity.
28 MODEEN BIOLOGY
at the Karlsakademie in Stuttgart. Whilst he was professor
of comparative anatomy at the Jardin des Plantes in Paris,
he published numerous important works. In 1812 he estab-
lished a new classification of the animal kingdom, which is
known as Cuvier's Theory of Types, and is based upon the
anatomical comparison of the various groups of animals.
According to it animals are divided with reference to their
structure into four main classes, which Cuvier called em-
branchements, but Blainville subsequently substituted the
name types. These are vertebrata, mollusca, articulata, and
radiata. Cuvier's Theory of Types was expanded and elaborated
by Karl Ernst von Baer (1792-1876), an Esthonian, the founder
of comparative embryology, whose theory of germinal layers
reduced the embryology of animals to a scientific system.
Cuvier's Theory of Types was not by any means his sole
contribution towards the development of modern zoology.
His comprehensive work 'Le regne animal' (1816), l in the
compilation of which he was assisted by many collaborators,
is the most important achievement in the domain of systematics
since the time of Linna3us. His ' Histoire des sciences naturelles,'
published after his death in Paris (1841-5), as E. Burckhardt
aptly remarks,2 presents the history of zoology and the natural
sciences in one vast frame, and is a monumental work of wide
scope. Cuvier devoted much attention also to fossil animals,
and between 1795 and 1812 he brought out several works on
the subject, laying down definite morphological principles to
be followed in comparing fossils with still existing animals of
the zoological system, and he thus became one of the chief
founders of modern palaeontology. His chief service to com-
parative biology was that he established the law of correlation,
i.e. he was the first to formulate the regular connexion of the
organs of any animal with one another, and with its habits
and environment. Although Cuvier did not regard as essential
the variations of form within his four great types, he was an
adherent of the theory of permanence, and in 1798 for the
first time he gave a clear concise statement of the meaning of
the * systematic species,' a definition that still holds good.
His views on the permanence of species brought him into
1 The fourth edition in eleven volumes appeared 1836-49.
2 ' Zur Geschichte der biologischen Systematik,' 390.
DEVELOPMENT OF CYTOLOGY 29
conflict with his contemporaries, Jean Lamarck and Etienne
and Isidore Geoffroy St. Hilaire, who upheld the transmutation
theory. The scientific struggle carried on by the members
of the French Academy ended for a time in the victory "of
Cuvier's opinion, but we shall have to recur in the ninth
chapter to the further history of the theory of evolution.
2. THE EARLY HISTORY OF CYTOLOGY
Hitherto, in speaking of the development of anatomy, we
have referred chiefly to macroscopic anatomy, which is not
dependent upon the microscope ; it is, however, to this instru-
ment that most of the progress made by modern morphology
is due.1
It was invented some hundreds of years ago, but not until
the nineteenth century did the real age of microscopical
research begin. As early as the year 1100 the Arab, Alhazen
ben Alhazen, described the magnifying power of a convex
lens. The English Franciscan, Koger Bacon, who lived 1214-
1294, and whom we have already mentioned (p. 16), seems
to have constructed complicated optical instruments. He is
said to have ground a piece of glass so that people saw wonder-
ful things in it, and ascribed its action to the power of the
devil. If this glass deserves to be called a microscope, the
honour of inventing this instrument would have to be ascribed
to Roger Bacon, but various nations claim to have given birth
to the inventor of it. The Italians say that either Galileo or
Malpighi invented it, but most people consider two Dutchmen,
Hans and Zacharias Janssen (1590), to be more justly entitled
to the credit of the invention. The name ' microscope ' was
first applied to the new instrument by Giovanni Faber in Rome
in 1625, and many improvements in it were made about 1646
by the astronomer Francesco Fontana in Naples. Malpighi
and Swammerdam certainly used the microscope in their
scientific work, and the Dutchman Anton Leeuwenhoek of
Delft (1632-1723), the ' Father of the Microscope ' as Schlater
calls him, used it in examining the ova and stings of bees, and
many other things connected with the anatomy of insects.
1 Cf. Dr. J. Peiser, ' Die Mikroskopie einst und jetzt,' in Natur und Schule,
IV, 1905, parts 10, 11.
30 MODERN BIOLOGY
By its aid he discovered infusoria, and drew the attention of
scientific men to a new world of diminutive creatures, our
knowledge of which was greatly increased by Christian Gott-
fried Ehrenberg in the middle of the nineteenth century. By
means of the microscope Leeuwenhoek was enabled to discover
the red-blood corpuscles and the transverse striation of the
muscular apparatus, and Hamm to perceive spermatozoa,
the key to those mysterious problems of heredity which
the greatest biologists of the present day are so eager to
solve.
Thus we see that microscopical anatomy made steady
progress, and advanced towards the marvellous triumphs
of modern histology and cytology. It was, however, a long
time before scientific men generally made use of the microscope ;
it is a surprising fact that even in 1800 it was altogether
neglected by Bichat, to wiiom we have already referred as the
founder of comparative anatomy. Consequently he could give
no account of cells, the smallest constituents of animal tissues,
although they had long before been recognised by other scien-
tific men who used the microscope.
Who discovered cells and the structure of organic tissues
out of cells ? In plants it is much easier to find the cells,
as they possess, as a rule, a more independent existence in
plants than in animals. It is therefore only natural that cells
were discovered first in botany. An Englishman, Robert
Hooke, gave cells their name because of their resemblance
to the cells of the honeycomb. In his ' Micrographia,' which
appeared in 1667, he gave the first illustration of a plant cell,
or rather cell-wall. The figure represents a bit of cork, along
which lengthwise run rows of black specks or cells. Hooke's
purpose in speaking of cells was not so much to add to the
scientific knowledge of botany, as to display the power of his
microscope, and so it is usual to ascribe the discovery of cells
to two other scholars, the Italian Malpighi (1674), whom we
have already mentioned, and the Englishman Nehemiah Grew
(1682). Their works on this subject appeared at almost the
same time, a few years after Hooke's ' Micrographia.' Ninety
years elapsed before another great scientist continued their
work. In 1759 Kaspar Friedrich Wolff published his remark-
able book ' Theoria generations,' in which he propounded new
EAKLY CYTOLOGISTS 31
ideas on morphogeny, and threw much light on the morphology
of organisms. His descriptions and illustrations show plainly
that he had studied the cells in both animal and vegetable
tissues ; he calls those in the former ' globules ' or ' spheres ' and
those in the latter ' utriculi ' or ' cells.' With regard to botany,
clear evidence that the vascular system of plants consists of
cells was adduced by Treviranus in his work ' Vom inwendigen
Bau der Gewachse ' (' The internal structure of vegetables'),
1808. The honour of having been the first to discover and
mention the nucleus of the living cell is generally ascribed to
an Italian-Tyrolese, Abbe Felice Fontana, 1781. However,
H. Bolsius, S. J.,1 has recently proved that the discovery was
made by Leeuwenhoek, the Dutch scientist already mentioned,
in 1686, about a century earlier.
The English botanist, Robert Brown, was the first to
discover (1833) the regular significance of the nucleus in its
relation to the cell, and for this reason many people regard
him as the real discoverer of the nucleus.2
It was not until Joseph von Fraunhofer in 1807 constructed
the first achromatic lenses, and thus greatly increased the
capabilities of the microscope, that modern cytology was
able to develop. It is a remarkable fact that just at this time
(1809) Mirbel, a Frenchman, began again to apply the name
' cell ' to the smallest elements in living organisms ; Malpighi's
word utriculus had long taken its place, but now, at the dawn
of modern cytology, the old name was revived, which Hooke
had given to these organic elements 150 years before. The
word ' cell ' is still in use, in spite of various attempts to
substitute some more modern name, such as protoblast (Kolliker)
and plastid (Haeckel). The study of the organic tissues
composed of cells was first designated Histology by Karl
Mayer in Bonn in 1819. Germany is therefore the real home of
both histology and cytology, and, as even the French scientists
acknowledge, both have grown and developed chiefly in
Germany.3
1 Antoni von Leeuwenhoek et Felix Fontana, ' Essai historique sur le revela-
teur du noyau collulaire,' Rome, 1903 (Memorie delta Pontificia Accademia
Romano, de.i Nuovi Lincei, XXI).
'2 Cf. 0. Herfcwig's Allgemeine Biologie (1906), pp. 5 and 27. Hertwig's
account of the history of the cell theory is very valuable, pp. 4, &c.
3 Cf. M. Duval, Precis d1 Histologie, Paris, 1900, p. 12.
82 MODEKN BIOLOGY
Everyone who has ever opened a modern book on
zoology or botany must know the names of Schleiden and
Schwann.
Matthias Jakob Schleiden, bom 1804 in Hamburg, became
the founder of modern botanical cytology when, in 1838, he
published his ' Beitrage zur Phytogenesis ' in Miiller's ' Archiv.' l
The zoologist, Theodor Schwann, born 1810 in Neuss, applied
the same principles to animal tissues in 1839, when he pub-
lished his ' Mikroskopische Untersuchungen iiber die Uberein-
stimmung in der Struktur und dem Wachstum der Tiere und
Pflanzen,' 2 and he added so much to Schleiden's work that we
generally speak of Schwann-Schleiden's theory of cells, or
cytology.3
In the case of every object of sense perception, human
knowledge invariably proceeds from the exterior to the interior,
from the shell to the kernel, and this is true of our knowledge of
cells. The dry walls of dead plant cells were what Hooke
called cells 250 years ago. Malpighi also studied particularly
the plant-cell, which is, as a rule, much larger and has thicker
and more conspicuous walls than the animal cell, and hence
it became the custom to regard the cellular membrane as the
essential part of the cell. Malpighi and Wolff represented the
cell as being practically an empty tube or bag — and this was
equivalent to mistaking a snail shell for a snail. Schleiden
and Schwann had a deeper insight into the truth, for they had
better aids to research at their disposal ; they discovered
that each tube or bag is filled with a fluid, and they noticed
the nucleus, though this had been discovered long before.
Their opinion was that the cell is a little vessel filled with
fluid in which a nucleus is suspended. Subsequent examina-
tion of young cells has shown that they have no real walls, and
the membrane appears to be an accidental part of the cell,
and thus the scientific idea of the cell advanced to the third
stage, at which it still practically remains. Franz Ley dig in
1 Cf. Jos. Rompel, S.J., ' Der Botaniker Matthias Jakob Schleiden '
(1804-81), in Natur und Offenbarung, I (1904), parts 4-7; see especially pp.
393-410.
2 ' Microscopical researches into the accordance in the structure and growth
of animals and plants. '
3 The botanists Treviranus and Meyen ought to be mentioned as having
prepared the way for Schleiden. Their works were published in 1808 and 1830
respectively.
.PROTOPLASM 33
1857 l and Max Schultze in 1861 3 denned a cell as a mass of
living protoplasm containing one or more nuclei.
The fluid contents of the cell were called protoplasm by
Hugo von Mohl in 1846, and the name has been universally
adopted, for it conveys an idea fundamental in biological
research.3 Dujardin in 1835 had named the same substance
sarkode, but no one now uses this word.
Von Mohl drew the attention of scientists to the movements
of protoplasm within the cells of plants, but they had been
noticed long before by Bonaventura Corti (1774) and C. L.
Treviranus (1807), and described as ' rotatory movements of
the cellular fluid.'
At this point the question naturally arises : What are the
chemical constituents of protoplasm ? In the first part of his
* Studien iiber das Protoplasma ' (1881), J. Keinke describes it
as * a mixture of numerous organic compounds.' Von Hanstein,
however, in 1879 defined protoplasm as an albuminous com-
pound or a mixture of albuminous compounds, and he proposed
to call it protoplastin. In his ' Lehrbuch der Zoologie,' R.
Hertwig says in a resigned way that we must acknowledge our
inability to determine the chemical characteristics of proto-
plasm. ' It is not known whether protoplasm is a definite
chemical body, which from its constitution is capable of infinite
variation, or whether it is a varying mixture of different
chemical substances. So, also, we are by no means certain
whether or not these substances (as one is inclined to believe)
belong to those other enigmatical substances, the proteids. We
can only say that the constitution of protoplasm must, with
1 The year 1859 or 1861 is generally given as the date when cytology entered
upon its third stage, therefore I will quote here a passage from Leydig's Lehrbuch
der Histologie des Menschen und der Tiere, published at Frankfurt a. M. in
1857. He writes as follows (p. 9) : 'To the morphological conception of a
cell belongs a more or less soft substance, originally almost globular in form,
containing a central body called the nucleus.' This, therefore, according to
Leydig's opinion in 1857 was the essence of the cell — he had already discarded
the membrane as non-essential — for he continues : ' The substance of the
cell frequently hardens so as to form a more or less independent outer layer
or membrane, and when this takes place the cell is technically said to consist
of membrane, substance, and nucleus.'
2 * Uber Muskelkorperchen und das, was man eine Zelle zu nennen habe '
(Archiv fur Anatomie und Physiologic, 1861).
3 Cf. 0. Hertwig, Allgemeine Biologie, p. 7, &c., for the history of the
protoplasm theory ; p. 12, &c., for investigations regarding the meaning
and nature of protoplasm.
D
34 MODEEN BIOLOGY
a certain degree of homogeneity, have a very extraordinary
diversity.' l
We may be satisfied to endorse J. Keinke's 2 remark that
our conception of protoplasm has always been morphological,
i.e. all we know about it is that it forms the primary substance
common to every living cell. A detailed account of all the
information hitherto acquired on the subject of the chemical
composition of protoplasm, as well as on that of the organisa-
tion of the cell and nucleus, and their reciprocal chemical
relations, will be found in E. B. Wilson's ' The Cell in Develop-
ment and Inheritance,' New York, 1902, chapter vii ; also in 0.
Hertwig's ' Allgemeine Biologie,' Jena, 1906, chapter ii, pp. 12,
&c. On pp. 18 et seq. Hertwig has shown very clearly that
the discovery of the substance and process of life is a vital
problem, and not merely an affair of chemistry and physics.
This subject will be discussed more fully in Chapters VII and
VIII.
Our knowledge of tissues and cells has been vastly increased
by means of microscopical research since the middle of the
nineteenth century. The names of the scientific men distin-
guished in this branch of research would make a long list ; we
can mention only the most eminent — Henle, Gerlach, Keichert,
Eemak, Leydig and Kolliker — some of the more recent
zoologists will be noticed later on. Botanists have been no
less zealous than zoologists in studying cells under the micro-
scope. We may refer to W. Hofmeister, A. Zimmermann, de
Bary and Sachs, as well as to the more recent students —
Pfeffer, Wiesner, and Strasburger.
3. METHODS OF STAINING AND CUTTING SECTIONS FOR
USE UNDER THE MICROSCOPE
Microscopical research has been greatly facilitated by the
discovery of the modern methods of chemical colouring.
As soon as definite colouring matters were applied to animal
and vegetable tissues, their structure became more plainly
visible, and the structure of the cell itself was revealed, for
the nucleus was found to absorb readily certain colouring
1 English translation, 1903, p. 61.
-' Einleitung in die theoretische Biologie, Berlin, 1901, p. 221.
STAINING AND CUTTING SECTIONS 35
matters which do not affect the protoplasm of the cell. The
nucleus was then seen to contain some darker coloured granules
or filaments or nucleoli, which suggested the idea that the
nucleus was not a simple but a composite body. In the same
way there appeared in the protoplasm darker coloured granules
or a network of filaments against a lighter background, and the
observation of these led to the discovery of the cell framework.
When the colouring process was applied to cells and nuclei
in course of division, pictures of wonderful beauty were revealed,
from which the laws of the division of the nucleus and of
fertilisation were learnt.
Gerlach in 1858 first used carmine as a stain for microscopical
purposes, and since his time the number and variety of colouring
methods have increased almost indefinitely. Gerlach used
carminate of ammonia, others have employed alum-carmine,
borax-carmine or carmalum, picro-carmine, &c.
The carmine stains were, however, discarded in favour of
haematoxylin, an excellent stain prepared from logwood
(Haematoxylon campechianum), which is applied in various
solutions and combinations, and is still much used in micro-
scopical work. The double stains obtained by using haema-
toxylin in conjunction with eosin or Congo red or saffranin
have lasted admirably, and have produced beautiful and
instructive plates, so that haematoxylin has not yet been
displaced by its numerous rivals prepared from coal-tar, and
known as aniline dyes. The colouring methods just mentioned,
and especially the use of haematoxylin and its combinations,
are of universal application, and can be employed for almost
all histological purposes, but there are also certain special
methods of staining particular tissues, especially those of the
nerves. Golgi, Kamon y Cajal, and Eanvier used solutions of
nitrate of silver, chromate of silver, and formic acid with
chloride of gold, in their attempts to overthrow the long-
established theory of a central nervous system, and thus
extended our knowledge of ganglion cells and their processes.
When Waldeyer formulated his theory of neurones in 1891,
and when soon after the theory of fibrils was put forward in
opposition to it,1 the chief arguments adduced in this scientific
1 At the seventy- second meeting of German naturalists and physicians at
Aix-la-Chapelle in 1900, a lively discussion of the two theories took place.
D 2
36 MODERN BIOLOGY
contest were supplied by observations on the nervous system,
rendered possible by the use of stains, — methods which Apathy,
Bethe, Nissl, Held, Bielschowsky and others have carried to
the utmost perfection. The anatomical and physiological
study of nerves owes much to Ehrlich, Eetzius and others,
who have succeeded in staining the nervous system of a living
animal with methyl blue, so that it has become possible to trace
the action of the finest fibres and terminations of the nerves.
Quite recently Carnoy and other cytologists at Louvain
have used methyl green, and have shown it to be of great
service in the development of biology, for it gives a vivid
colour to the nucleus of a cell still living, thus rendering visible
the most minute details of its structure.
As special stains, used in studying the stages of division
of the nucleus in the process of mitosis, we may mention parti-
cularly Heidenhain's use of iron alum with haematoxylin and
Plattner's metallic nuclear black.
All these colouring methods would avail but little, however,
if scientists had not at their disposal a means of cutting organic
tissues, as well as entire animals and plants, after artificially
hardening them, into layers so thin that light can penetrate
them and make their wonderful construction visible under
the microscope. The art of cutting sections is as indispensable
as the art of staining, and it is by means of both in conjunction
that microscopic anatomy has been enabled to make its
extraordinary progress in recent times. It owes the one to
chemistry, and the other to modern mechanics, which created
the microtome and placed it at the service of biology.
The microtome is a mechanical apparatus which passes an
extremely sharp knife in a definite direction over an object
embedded in paraffin or celloidin or some similar embedding
substance, and at the same time a movable plate provided with
a scale automatically regulates the thickness of each section.
As at each turn of the plate, about a given angle, the knife
is lowered, for instance, y^mm., or (in other microtomes) the
object is raised Yoo"mm'> a skilful worker is able to obtain an
M. Verworn supported the theory of neurones in his lectures, ' Das Neuron in
Anatomie und Physiologie' (reprinted at Leipzig, 1901). See also Fr. Nissl,
Die Neuronentheorie und ihre Anh'dnqer, Jena, 1903 ; M. Wolff, ' Neue Beitrage
zur Kenntnis des Neurons ' (Biolog. Zentralblatt, 1905, Nos. 20-22) ; Wasmann-
Gemelli, La Biologia Moderna, Florence, 1906, p. 44 note.
TEBMITOXENIA 37
unbroken series of sections, each y^mm. in thickness. In the
same way he can obtain sections of -^^mm., g^
if he requires them. The microtomes most generally used at the
present day are those made by E. Jung in Heidelberg. Micro-
tomes on another system were devised by Professor Hatschek
and made by Jensen in Prague ; in these the knife does not
move up and down along an inclined surface, as it does in
Jung's apparatus, but it moves backwards and forwards over
a horizontal surface. With the latter I have succeeded better
than with the former, and have even prepared very thin and
regular sections cut through the hard chitin integument of
beetles and other insects. There are also lever microtomes,
English microtomes with a pointed spindle, and Minot's new
American microtomes intended to cut sections of larger
objects. The construction of these ingenious instruments has
in the last few years become a special branch of mechanics,
and interesting accounts of their great perfection may be found
in the illustrated price-lists issued by E. Jung and Walb in
Heidelberg, Eeichert in Vienna, and others.
4. THE MICROSCOPIC STUDY OF THE ANATOMY AND
DEVELOPMENT OF A DIMINUTIVE FLY
(Termitoxenia.) (PLATE V)
I should like to illustrate the great advance made in bio-
logical research through the adoption of modern methods of
staining and cutting sections, and my illustration, derived
from my own work, will take my readers out of the gloom of
theories into the cheerful atmosphere of practical results.
I am at this moment studying some extremely small insects
only 1-2 mm. in length, belonging to the order of Diptera.
They have a relatively enormous white abdomen, and in the
course of the last few years have been found in the nests of
termites in South Africa, the Soudan and India, by G. D.
Haviland, Dr. Hans Brauns, J. B. Heim, J. Assmuth, S.J.,
and Y. Tragardh.i
1 In subsequent chapters I shall have occasion to refer repeatedly to this
remarkable fly. belonging to the family of Termitoxeniidae. An account of it
is given in Chapter X, ' Theory of Permanence or Theory of Descent,' and
illustrations will be found on Plate V.
38 MODEBN BIOLOGY
Diptera of the normal type have two wings, but in their
stead this little creature (which I have described under the
generic name Termitoxenia) l has peculiar appendages to the
thorax (Plate V, figs. 1, 2, 4, 5) which are morphologically
homologous with wings, but have actually so developed as to
serve quite other purposes than that of flight, for which their
narrow, club-shaped or hooked form and their horny structure
render them altogether unsuitable. They are, however, well
adapted to perform a number of new functions, closely connected
with the insect's habit of living among the termites. The
appendages to the thorax of the Termitoxenia serve as organs of
transport, by which these little inquilines are picked up and
carried about by their hosts ; they serve to maintain the
fly's equilibrium and enable it to balance itself when it walks,
as otherwise the enormous size of its body would render walk-
ing very difficult ; they are sense organs, supplying the creature
with a great many percepts by way of touch ; they are organs
of exudation, through which it emits a volatile element in
its blood as a pleasing stimulant to the greed of its
hosts ; finally they resemble supplementary spiracles, that to
some extent are like the tracheal gills of the insect's earliest
aquatic ancestors.
These little termitophile Diptera are indeed a store-house
of anomalies, whether we consider them from the point of view
of morphologists, anatomists, evolutionists, or biologists.
They are exceptions to the laws of entomology. They are
not merely Diptera without wings, but they are flies without
the larval and pupal stages, and are actually insects having
neither male nor female !
In order to shorten the lengthy and complete process of
metamorphosis undergone by other Diptera, the Termitoxenia
lays comparatively enormous eggs, from which is hatched not
a larva, as is the case with other flies, but a perfect insect,
1 * Termitoxenia, em neues fliigelloses, physogastres Dipterengenus ain
Termitennestern,' Part I (Zeitschrift fur wissenschaftliche Zoologie, LXVII,
1900, pp. 599-618 with plate XXXIII) ; Part II (ibid. LXXX, 1901, pp.
289-98) ; ' Zur naheren Kenntnis der termitophilen Dipterengattung
Termitoxenia ' (Verhandl. des V. internationalen Zoologenkongresses zu Berlin,
August 1901, pp. 852-72 with one plate) ; ' Die Thorakalanhange der Ter-
mitoxeniidae, ihr Bau, ihre imaginale Entwicklung und phylogenetische
Bedeutung' (Verhandl. der deutschen Zoolog. Gesellschaft, 1903, pp. 113-120,
with plates II and III).
TEEMITOXENIA 39
the imago form, still in a stenogastric or thin-bodied con-
dition. To compensate for the absence of metamorphosis,
the Termitoxenia, as imago, undergoes a postembryonic de-
velopment, for its organs of generation, especially the single-
tubed ovaries, its fat-body, consisting of large cells joined
together end to end, its abdominal muscular system, and even
the outer skin of the abdomen, receive their final form only in
the course of a long process of growth. Each of these insects
is moreover a complete hermaphrodite, there are no distinct
males and females at all. The youngest imagines have some
quite undeveloped ovaries, such as occur in the larvae of other
Diptera, but even in the youngest specimens the male generative
glands and the bundles of spermatozoa connected with them
are well marked, although they subsequently become atrophied,
when the spermatozoa have ripened, whilst the ovaries develop.
We have, therefore, here an instance of what is called prot-
andric hermaphroditism, which regularly allows first the
male and then the female generative glands to develop in the
same individual, so that the Termitoxenia is something quite
unique in insect biology.
It is most interesting to trace the development of the
ovaries. (See Plate V, fig. 6.) Each one consists of a single
egg-tube — a phenomenon long sought in vain among insects
by the upholders of the theory of evolution, until Grassi
discovered it occurring in the very rudimentary ground-flea
(podura), belonging to the genus Campodea.
This single egg-tube on each side of the Termitoxenia' $
body is, in the case of the youngest specimens, merely one
single long terminal chamber, filled with apparently un-
differentiated little nuclei.1
In course of time the egg-tube contracts in between the
eggs, and forms a long series of ovarian chambers, those at the
lower end of the ovary being the largest. In each of these
chambers the elements of the ovary differentiate themselves
into nutritive cells and true egg-cells, so that each chamber
eventually contains several large cells, one of which develops
1 I use the word * apparently ' advisedly, for in one of his recent works
('Untersuchungen iiber die Histologie des Insektenovariums,' in the Zoologische
Jahrb'ucher, Section for Anatomy, 1903, part 1), Gross has proved that the
epithelial cells and those that eventually become germ-cells differ from one
another even in the terminal chamber.
40 MODERN BIOLOGY
more rapidly than the rest and becomes the egg. The other
cells in the same chamber serve as its food, or, in scientific
language, a fusion takes place of the egg-cell with the nutri-
tive cells, the substance of the latter being gradually absorbed
into that of the former, and transformed into tiny yolk-
capsules collected round the germinal vesicle of the young egg.
Thus the egg is nourished and it continues to grow until it
occupies about a quarter of the entire abdomen of the full-
grown insect. (Plate V, fig. 6 ov.) By this time it has taken
up enough yolk-material to serve for the whole embryonic
development until it reaches the stage of imago, when it must
make its own way in the world. It is fertilised, and, passing
along the ovarian duct, it is laid among the eggs of the
termites.
The history of the development of a fly belonging to the
sub-genus Termitomyia is somewhat different, but still more
extraordinary. In this case the egg, whilst still within the
parent's body, becomes an embryo, wilich develops until
it reaches the form of a stenogastric imago. Therefore this
sub-genus lays no eggs at all, but brings forth its young
alive. These viviparous insects are a worthy contrast to the
oviparous mammals, such as the ornithorhynchus and the
Australian ant-eating Echidna.
There is a regular correlation between all the points on which
the remarkable anatomy and development of the Termitoxenia
differ from those usual among insects. The fact that each
ovary has only one egg-tube facilitates the formation of eggs
few in number, but large and rich in yolk. The large size and
richness in yolk of the eggs render the omission of the larval
and pupal stages possible, and so the whole process of develop-
ment is conveniently shortened and simplified, and the imago
is produced out of the egg or rather out of the embryo.
Moreover, in the case of the Termitoxenia, the complicated
process of assigning sex to the individual is simplified in a
form that is perfectly ideal for insects, as each individual
fulfils both functions. And all these wonderful peculiarities
in the morphology, development, and biology of the Termito-
xenia, its physogastria and its ametabolia, its growth as an
imago and its hermaphroditism, the shape of its appendages
to the thorax and the formation of the parts of its mouth —
USE OF THE MICROSCOPE 41
for it has a long proboscis for sucking the tender, juicy young
of the termites — all these are closely connected with and
dependent upon the affection of these Diptera for the termites !
And how, it may be asked, do we know all this ? Have
observations been made in India and Africa regarding the
habits of these diminutive creatures, and has their development
been studied for years in artificial nests of termites ? By no
means. The discoverers of the six known varieties of Termito-
xenia merely established the fact that they always are found
in the nests of certain kinds of termites and among their eggs
and larvae. The inquilines and their hosts were sent to me
in alcohol or formol. But the further question arises, how
can it be possible, in that case, to make such definite and
apparently rash statements as to the habits of these creatures ?
They are so small, that even a powerful magnifying glass
scarcely enables us to distinguish the details of their exterior
configuration ; even under the microscope it is difficult to
make out the halteres or balancers, which are placed behind
the thoracic appendages, and prove that the latter morpho-
logically correspond to the wings of Diptera and do not point
to a coalescence of wings and halteres.
What scientific evidence is there, then, in support of the
account just given of the anatomy, development, and biology
of Termitoxenia ?
The account is based- on the results obtained by modern
methods of using stains and cutting sections. The series of
sections of Termitoxenia supply us with material for studying
its anatomy, development, and biology.
So far I have obtained by means of the microtome complete
series of sections of sixty specimens of five species of Termito-
xeniidae of various ages, and I have also cut sections of a
number of eggs of various species ; as a stain I have generally
used a double preparation of haematoxylin (Delafield's method)
and eosin.1
The total number of sections thus prepared amounts to
10,000. Each specimen submitted to microscopical examina-
tion furnishes a series of from 80 to 200 sections of y^ mm. in
thickness ; the number varies according as the sections are
1 Or a double stain obtained by using haemalum (Meyer's method) and
orange eosin, &c.
42
MODEEN BIOLOGY
longitudinal or transverse. Each series of sections therefore
forms a book of from 80 to 200 pages, on which are recorded
in unbroken sequence the whole exterior and interior morpho-
logy of the specimen, and this record is legible under the
microscope. If the sections of various kinds of Termitoxenia at
different ages, and also of their respective eggs, are compared
with one another, the morphological volumes come to form
a library containing an account of the Termitoxenia' $ develop-
ment. As, however, almost every point in the anatomy
i. JT. sr JF. v. H m m.
1
/
7
11
i1)
tf
J/
n
43
I
I
8
w
to
U
31
18
44
3
9
15
11
*?
S3
39
4S-
4
10
16
it
HI
3'/
40
46
£
//
'?
13
19
•3f
t*l
tlf
6
n
It
14
1C
36
41
W
IT m or v.
II.
FIG. 1. — Scheme of a series of sections of Termitoxenia Heimi Wasm.
and development of these tiny creatures is of significance in
their habits, this library supplies also trustworthy information
for their whole biology.
The accompanying illustration (fig. 1) represents a series
of sagittal sections of Termitoxenia Assmuihi. It consists of
the longitudinal sections of specimen No. 13 of this variety,
arranged upon two slides (i and ii). The Koman numerals on
each slide refer to the sequence of the rows of sections, the
Arabic numerals to the sequence of the sections in each row.
Thus the series begins with No. 1 on the first slide and ends
with No. 96 on the second. No. 49, the first on the second
USE OF THE MICKOSCOPE 43
slide, is a section cut from the middle of the creature's body —
a photograph of it will be found on Plate V, fig. 6, at the end
of the book.
I need hardly say that a great expenditure of time and
trouble is needed, not merely to make such series of sections,
but far more to study them with success. The instances of
morphological and biological conformity to law, which a
scientist can discover, seem to be written in a mysterious
cipher, the key to which is found only by careful study. No
one, therefore, will be astonished to hear that I have spent
years on my study of the Termitoxenia, especially as I had
not only to describe my microscopical results in words, but
to reproduce them by means of drawings or photographs
upon a series of carefully executed plates.1
The marvellous beauty of the various sections is no less
noticeable than their scientific value in biological research.
The material for several series of sections of Termitoxenia
Heimi and Assmuthi was supplied me by J. B. Heim, S.J.,
Missionary in India, and J. Assmuth, Professor at St. Francis
Xavier's College in Bombay. The creatures reached me in very
good preservation, having been killed and hardened in a
mixture of alcohol and formalin. The sections, stained with
haematoxylin and eosin, or some similar double stain, are
so beautiful that they cannot fail to arouse admiration in any
one who sees them, even in the mind of one who regards
all insects alike as ' vermin.' Eosin stains the protoplasm
of the tissues various shades of light red, whilst the' nuclei,
which chiefly serve to differentiate the various kinds of tissue,
are coloured light or dark blue by means of haematoxylin or
haemalum ; the whole picture displays a delicacy of design
and a beauty of colouring such as no artist's skill could repro-
duce in perfection. The most complex and most highly
coloured pictures are formed by sections showing the various
stages of development in which the mysterious biological
processes of cell-division, cell-multiplication, and cell-growth —
those elementary functions of life — are most active.
Modern microphotography will, perhaps, succeed in fixing
1 A fuller account of my work will appear in the Zeitschrijt fur wissen-
schaftliche Zoologie. A resume of the results obtained hitherto was given in
an address delivered at the fifth International Zoological Congress in Berlin,
August 1901.
44 MODERN BIOLOGY
microscopical sections with all their gorgeous colouring directly
upon photographic plates. If this is ever done, it will be of
the utmost scientific importance, as the precise shades of
colour in the nuclei and other parts of the tissues often give
a trustworthy clue, of great assistance in histological and
cytological research.
A learned professor of theology, on seeing some series of
sections of the Termitoxenia, remarked very aptly that micro-
scopical research, by means of modern methods of staining and
cutting sections, had become a second creation, creatio secunda,
revealing to us for the first time all the marvels which God
at its first creation had concealed within the body of this
diminutive fly.
In order to give my readers a wider idea of the application
of microscopical study to our investigations into animal
biology, the following remarks may be added. Let us suppose
that some one asks : ' Why do ants and termites show such
energy and pleasure in licking their " true inquilines " ? Upon
what does the satisfaction depend which they derive from so
doing ? '
Before this question can be answered, a reply must be given
to another, viz. : ' What tissues underlie the external exudatory
organs, which lead to the process of licking the inquilines ? '
With a view to answering this latter question I have, in the
course of the last ten years, prepared about 20,000 sections of
various kinds of inquilines among arits and termites (they are
chiefly beetles), and studied their tissues under the microscope.
In this way I have arrived at the following conclusion : — the
exudation of true inquilines, with which they repay their
hosts for their hospitality, is partly a direct and partly an
indirect product of adipose tissue ; when it is indirect, it is
partly a glandular secretion and partly an element in the blood
plasm of the inquiline.1
We are therefore now in a position to divide the genuine
inquilines among ants and termites into various classes according
to their exudatory tissues, and thus have made a perceptible
step towards solving the mystery of true guest-relationship.
1 Articles on this subject appeared in the Biologisches Zentralblatt, 1903,
Nos. 2, 5, 6, 7, 8, under the heading : ' Zur naheren Kenntnis des echten
Gastverhaltnisses (Symphilie) bei den Ameisen- und Termitengasten.'
KECENT CYTOLOGISTS 45
5. KECENT ADVANCE IN MICROSCOPICAL KESEARCH
After this little digression let us return to the historical
development of modern histology and cytology.
Improvements in the microscope itself, the chief implement
in our research work, have kept pace with the adoption of
better methods of staining and cutting sections.
As a result of very careful physical studies, Abbe of Jena
devised an apochromatic objective, calculated exactly with
reference to its refractive and dispersive power. This was
worked out by Schott & Co., in Jena, and then further per-
fected by Karl Zeiss, the able optician in Jena. The apo-
chromatic objective has been imitated with various degrees
of success by other German and foreign firms. Its introduc-
tion, and that of the corresponding compensating ocular or
eye-piece, mark an important stage in the development of the
microscope. Speaking from my own personal experience,
I can safely assert that the pictures produced by this system
of lenses are infinitely clearer than those produced by the
achromatic objectives and Huygenian oculars previously
in use. It is now possible to see every detail in the structure
of tissues even when magnified 1500-2000 times.
This advance in optical appliances has enabled modern
cytologists to study the most delicate construction of a resting
cell, as well as the processes of division and fertilisation,
and to discover the laws governing these most important
phenomena of life.
Histology and cytology made great progress during the
latter half of the nineteenth century in other countries as well
as in Germany, where they had their birth, and where they
grew to the rank of independent sciences, in consequence of the
research work done by Schleiden, Schwann, Kemak, Leydig, .
and Max Schultze.
I can mention the names of only a few of the more recent
workers in this department of science ; in Germany, besides
Leydig and Max Schultze, we have Strasburger, Weismann,
Memming, Biitschli, Henking, Heidenhain, Boveri, A. Brauer,
Keinke, the two Hertwigs, Haecker, Erlanger, 0. vom Eath,
Schaudinn, Khumbler, &c. ; in Bohemia, Eabl ; in Hungary,
46 MODEEN BIOLOGY
Apathy, who has made nerve-cells his special study ; in
Switzerland, Fol ; in France, Kanvier, Balbiani, Giard,
Maupas, Kunstler, Guignard, Armand Gautier, and Yves
Delage ; in Belgium, van Bambeke, E. van Beneden, and the
great cytologists of the Catholic University of Louvain, viz.
Abbe Carnoy, the author of ' Biologie cellulaire,' and his pupils,
of whom G. Gilson, A. van Gehuchten, and Abbe Janssens are
well known through their important publications ; in Spain,
Bam<5n y Cajal ; in Italy, Giardina ; in Great Britain and
Ireland, A. Sedgwick, Moore, McGregor and Dixon ; in Sweden,
Ketzius and Murbeck ; in Bussia, Kowalevsky, Tichomirow,
Nawaschin and Sabaschnikoff ; in North America, Ch. Sedg-
wick Minot, Chittenden, E. B. Wilson, Th. H. Montgomery and
Osborn ; lastly, in Japan, Chiyomatsu Ishikawa, director of
the zoological institute of the Imperial University of Tokio.
We may therefore well say that all civilised nations of the
present time have contributed to the development of modern
histology and cytology.1
In order that my readers may not regard the Jesuits as ' mediaeval
obscurantists ' trying to stem the advance of science, I may be
allowed to add that a Dutch Jesuit, H. Bolskis,2 has done much to
increase our knowledge of the microscopical anatomy of Hirudines
or leaches, and has shown himself an authority of the highest
rank on this subject. A modern morphological and biological
1 This is of course true, not only with regard to the morphology of the
cell, with which we are now chiefly concerned, but also with regard to its
vital phenomena, especially the processes of cell division and fertilisation,
to which we shall have to refer later. I should like to draw particular attention
to Carney's Biologie cellulaire. 1884, which unhappily was never completed;
also to Oskar Hertwig's Allgemeine Anatomie und Physiologie der Zelle, 1893 ;
and Max Verworn's Allgemeine Physiologie, the third edition of which appeared
in 1901, and deals mainly with cellular physiology. I regret that Verworn's
work is not altogether free from phrases suggestive of Haeckel's influence and
wanting in scientific dignity. For instance, on p. 214, in speaking of par-
thenogenesis among the lower animals, he refers to ' the ancient legend of the
Immaculate Conception.' The author seems to be as far as Haeckel from
a comprehension of the dogma of the Immaculate Conception.
2 ' Nouvelles recherches sur la structure des organes segmentaires des
Hirudinees,' 1890 ; ' Les organes cilies des Hirudinees,' 1891 ; ' Le sphincter
de la Nephridie des Gnathobdellides,' 1894 ; * La glande impaire de 1'Hae-
mentaria officinalis,' 1896 ; ' Recherches sur 1'organe cilie de 1'Haementaria
officinal!*,' 1900 (this article appeared in La Cellule). I might also mention
a number of other articles which the same author contributed to the Annales
de la Societe scientifiqiie de Bruxelles, to the Memorie della Pontificia Accademia
dei Nuovi Lincei, to the Zoologischer Anzeiger (Leipzig), and the Anatomischer
Anzeiger (Jena), &c.
JESUIT SCIENTISTS 47
work, universally regarded as a masterpiece, has been written
by J. Pantel, a French Jesuit, on the larva of Thrixion hali-
dayanum ; l and no less excellent are an anatomical and histological
study of the anal glands of beetles by a Belgian Jesuit, Fr. Dierckx,2
and a biological and anatomical study of walking stick insects by a
French Jesuit, R. de Sinety.3
These publications, as well as most of the works of Carnoy,
Gilson, van Gehuchten and Bolsius, appeared in La Cellule, a
periodical published by the Cytological Institute of the Catholic
University of Louvain, a society founded by Abbe Carnoy. This
periodical is highly esteemed by German scientists, and forms a
complete refutation of the old fiction that Catholics, and especially
those of Romance nations, must needs be bad men of science. In
the sixth chapter I shall have to refer to some articles on the
chromosomes in the eggs of Selachii and Teleostei by J. Marechal,
a Belgian Jesuit, and among Italian scientists, a Franciscan,
Dr. Fra Agostino Gemelli, has written some excellent works on
anatomy and histology during the last few years.
1 ' Le Thrixion halidayanum, Rond. : Essai monographique sur les caracteres
exterieurs, la biologie et 1'anatomie d'une larve parasite du groupe des Tachi-
naires,' 1898 (La Cellule, XV).
2 ' fitude comparee des glandes pygidiennes chez les Carabides et les
Dytiscides,' 1899 (La Cellule, XVI) ; ' Les glandes pygidiennes des Coleopteres,'
2nd memoire, 1900 (ibid. XVIII).
3 Recherches sur la biologie et Fanatomie des Phasmes, Lierre, 1901. This
work contains splendid illustrations ; in the eighth chapter the author dis-
cusses the karyokinetic processes in the spermatogenesis of Orthoptera, a
subject of peculiar interest as throwing light on the accessory chromosomes.
CHAPTER III
MODERN DEVELOPMENT OF CYTOLOGY
1. THE CELL, A MASS OF PROTOPLASM WITH ONE OR MORE NUCLEI.
Cells of various shapes and dimensions, giant and dwarf cells (p. 49).
Uninuclear and multinuclear cells (p. 53).
2. THE STRUCTURE OF THE CELL EXAMINED MORE CLOSELY.
Hyaloplasm and spongioplasm ; theories regarding the structure of the
latter; filar and reticular theory (p. 56); alveolar theory (p. 57);
granular theory (p, 59). Reinke and Waldeyer's scheme for reconciling
these theories (p. 60).
3. THE MINUTE STRUCTURE OF THE NUCLEUS.
Chemical and physical theories of colouring (p. 61). Fischer's theory of the
polymorphism of protoplasm (p. 62).
4. SURVEY OF THE HISTORICAL DEVELOPMENT OF THE MORPHOLOGY OF
THE CELL.
The cell not a simple, but an extremely complex formation (p. 65).
1. THE CELL, A MASS OF PROTOPLASM WITH ONE
OR MORE NUCLEI
ON p. 33 we have seen that Franz Leydig in 1857 and Max
Schultze in 1861 denned the cell as a small mass of proto-
plasm containing one or more nuclei. This has remained to
the present day the fundamental idea of the cell, as we may see
on referring to the definitions of it given by Richard Hertwig in
the seventh edition of his ' Lehrbuch der Zoologie,' l Matthias
Duval in the second edition of his handbook of histology,3 and
Oskar Hertwig in his ' Allgemeine Biologie.' 3 With regard to
this definition there is almost unanimous agreement on the part
of the chief cytologists of various nations, and this is a very
significant fact, especially as modern cytology is a much
debated subject. If it is possible in any branch of knowledge
to speak of a sententia communis doctorum, we may regard
1 Jena, 1905, p. 50 : ' The cell is a little mass of protoplasm containing
one or more nuclei.'
2 Precis d'Histologie, Paris, 1900, p. 26 : ' La cellule est essentiellement
une petite masse de protoplasma avec un noyau.'
3 1906, p. 27 : ' The nucleus is just as essential to the existence of a cell
as is the protoplasm.' Cf. also the more detailed account given by 0. Hertwig
in the third chapter of the same work.
48
THE CELL 49
the definition of a cell as such in a very conspicuous
degree.
I must acknowledge, however, that this unanimity exists
among zoologists and histologists more than among botanists.1
In many of the smallest forms of plant life, especially in
many bacteria, the presence of a true, clearly differentiated
nucleus has not yet been established.3 I use the words ' true,
clearly differentiated nucleus ' advisedly, for cytologists are
more and more adopting the opinion that even in those micro-
organisms previously regarded as devoid of nucleus the
nuclear substance is present, though divided into smaller
particles, which E. Hertwig has designated chromidia? This
opinion gains support from the discovery of a true nucleus
existing at a definite stage in the formation of the spores of
the Bacillus Butschlii.41
We shall have to return later on (Chapter VII) to the most
recent investigations made by biologists on the subject of the
absence of nucleus in these extremely small forms of life. For
the present it is enough to say that the idea of a living cell
involves that of a nucleus, either as a whole or in parts, but
the chromatophores that exist in most plant cells besides the
cytoplasm and the nucleus are certainly not essential to the
existence of the cell, for they are absent in Bacteria and fungi,
and in all animal cells.5
Let us now proceed to study the structure of a cell more
in detail.
In shape and size cells vary greatly. The normal shape of
a free cell, not united with others of the same kind to form a
tissue, is spherical, but even the unicellular plants and animals
are seldom quite round, and cells united to form tissues still
less often approach a spherical shape ; they are rounded, or
oval, or cylindrical, or cubical, or pentagonal, or hexagonal ;
1 Cf. Lehrbuch der Botanik fur Hochschulen by Strasburger, Noll, Schenk and
Karsten, 6th edit,, Jena, 1904, pp. 46-7, 270, 274, where it is stated that the
presence of a nucleus in the lowest plants (Cyanophyceae and Bacteria) is
still uncertain. (English translation, 3rd edit. 1908, pp. 53 and 332.)
2 Cf. J. Reinke, Einleitung in die theoretische Biologie, 1901, pp. 256, &c.
3 R. Hertwig, ' Die Protozoen und die Zellentheorie ' (Archiv fur Protisten-
kunde, I, 1902, pp. 1-40).
4 Fr. Schaudinn, ' Beitrage zur Kenntnis der Bakterien und verwandter
Organismen,' I. Bacillus Biitschlii, n. sp. (Archiv fur Protistenkunde, I,
pp. 306, &c.).
3 Cf. Strasburger, &c., pp. 46, 47 (Eng. trans, p. 53).
50
MODERN BIOLOGY
sometimes they are of almost the same thickness in all three
dimensions, at other times they are flattened out like those of
the pavement epithelium (fig. 2d), or extraordinarily long, like
nk
FIG. 2.
Magnified 230 times [Zeiss D, Ocul. 2].
All the figures have been prepared with the camera lucida from series of
sec.tions-
KEY TO FIG. 2.
a = Giant cell containing two nuclei from the abdominal fat-body of a
physogastric specimen of Termitoxenia Heimi Wasm.
zk, zk = nuclei.
b = young egg of Termitoxenia Heimi Wasm. The egg -cell is still enclosed
within the follicular epithelium of the ovary. (From a sagittal
section of a physogastric specimen of Termitoxenia Heimi. )
ep — epithelial cells of the one-layered follicle.
zk = nuclei of the epithelial cells.
kb — germinal vesicle of the egg.
kf = nucleolus of the germinal vesicle.
dd = vitelline spherules.
nk = remains of the nucleus of a nutritive cell, the material of which has
served to form the yolk.
c = three unicellular muscular fibres from the cutaneous muscular apparatus
of the abdomen of a stenogastric specimen of Termitoxenia (Termi-
tomyia) mirabilis Wasm.
zk = nucleus.
d = two epithelial cells from the hypodermis of the abdomen of a steno-
gastric specimen of Termitoxenia Heimi.
zk = nucleus.
the spindle-shaped cells of the smooth muscular fibres, and
the still more slender cells that form the transversely striated
muscular fibres (fig. 2c).
THE CELL 51
As a rule, the cells that make up tissues have no prolonga-
tions, but in making this statement I am not challenging
Heitzmann's discovery (1873) of protoplasmic cell-bridges.1
Many cells, however, possess long offshoots, which give them
a ramified appearance ; this is particularly the case with nerve-
cells, and is closely connected with their telegraphic functions.
The shape of the nucleus varies less than that of the cell,2
it is mostly round or oval, although other shapes not in-
frequently occur. Very remarkable are the branching nuclei
of the Malpighian tubes in certain caterpillars, and the nuclei
resembling a string of beads in some unicellular Stentors.
In speaking of the size of a cell, we must have a standard
by which to measure it. In this respect little cells resemble
so-called tall men ; we cannot measure either by any usual
method, an old-fashioned foot-rule and a modern metre
measure are equally out of place. Cells have to be measured
under the microscope, and the following method is the simplest.
The number of times that the object is magnified is carefully
noted, and a sketch of the cell is made on paper by means of a
camera lucida. This sketch is then measured with a very
exact millimetre measure, and the number thus obtained is
divided by that of the magnifying power. For instance, if
a cell, magnified 230 times, measures 23 mm., its real magni-
tude is O'l mm. This would be a giant cell if it belonged to
animal tissue. Such giant cells as this (cf. fig. 2a) compose
the abdominal fat-body of the Termitoxenia, a variety of
Diptera living among termites, as we have already seen (pp. 37,
&c.). Most cells in animal tissues are dwarfs in comparison,
and dwarfs among dwarfs are the average blood corpuscles,
especially of insects, and the spermatozoa of most animals.
Therefore, as a constant unit for microscopical measurement
of cells, the thousandth part of a millimetre has been adopted,
which is known as a micromillimetre or micro, and is designated
by the letter JJL. The giant cells of the Termitoxenia' s fat-
body have a diameter of lOOyu,. Cells of ID//, (e.g. figs. 2d
1 A further account of these protoplasmic cell-bridges will be found in
Wilson, The Cell, pp. 56, 60, where there is a careful discussion of the evidence
for their existence among very various kinds of plant and animal cells. See
also 0. Hertwig's Allgemeine Biologie, pp. 400, &c.
2 For the shape, size, and number of nuclei, see 0. Hertwig, Allgemeine
Biologie, pp. 28, &c.
E 2
52 MODEKN BIOLOGY
and 2b, &c.) are of medium size, so the former may well be
called gigantic.
But there are some animal cells far larger than these, viz.
the egg-cells. These are the largest in the animal kingdom.1
The ripe egg-cell of a diminutive insect such as the Ter-
mitoxenia, barely 2 mm. in length, measures almost 1 mm., i.e.
it is half as long as the creature's whole body. The eggs of
this fly are reckoned, therefore, among the relatively largest in
the entire animal kingdom ; the absolutely largest occur
among birds ; it is in fact possible to use a yard measure to
ascertain the size of the eggs of the ostrich or moa. A bird's
egg before fecundation consists of one huge cell, but to the
egg-cell belong in this case not only the germinal vesicle,
which represents the nucleus of the protoplasmic part or
formative yolk of the egg-cell, but also a quantity of nutritive
yolk or deuteroplasm,3 which is really the yolk of the bird's
egg. The white of the egg and the shell appear only after
fecundation, and are outer coverings, and not parts at all of
the egg-cell. Animal egg-cells owe their conspicuous size to
the presence of deuteroplasm or nutritive yolk, which is found
in the eggs of all creatures that are oviparous and not vivi-
parous. In the case of the former a considerable quantity of
nutritious matter must be stored up in the egg itself, in order
that the embryo may develop. My readers must not, how-
ever, fancy that, when they see a new-laid hen's egg, they have
only one huge egg-cell before them ; for, quite apart from the
above-mentioned exterior coverings, which grow before the
egg is laid, the egg itself is already fertilised, its germinal
vesicle has become a germinal disc, i.e. a still very diminutive
embryo chick, consisting of numerous segmentation cells, and
the huge egg serves as its lodging and store-room during its
further development.
In order to illustrate the various shapes and sizes of the
cell by examples, I have reproduced some cells of Termitoxenia
on p. 50. To the explanations already given I may add that,
1 Very large cells constitute the plasmodia of the Mycetozoa, which are
also reckoned among the lower orders of plants and called Myxomycetes,
whilst by others again they are classed with the Protozoa. Cf. R. Hertwig,
Lehrbuchder Zoologie, 7th edit., 1905, pp. 49 and 168 (Eng. trans, pp. 60, 61, 198).
2 E. van Beneden called the nutritive yolk 'deutoplasm,' to contrast it
with protoplasm ; ' deuteroplasm ' is a more correct form of the word.
THE CELL 53
with a view to economising space, I chose for Fig. 2b not a
ripe and fully developed egg-cell, but a young cell, still
surrounded by a thick follicle of epithelial tissue, and having
at its lower end the remains of an incompletely consumed
nutritive cell. As the latter is already incorporated with the
substance of the egg, the young cell (without the epithelium)
measures 135//, in length and 95//, in breadth. A ripe egg-
cell of the same kind of Termitoxenia would, if drawn on the
same scale (magnified 230 diameters),* occupy a space of
2 dm., and cover a whole page of this book.
Some plant cells are also very large ; for instance, there
are bast-cells 2 dm. in length and of considerable breadth.
Among the lower plants too, such as the Caulerpa (one of the
Algae), there are cells several decimetres in length; in fact,
according to J. Reinke and other botanists, the whole plant with
its root, stem, and leaves consists of one cell with many nuclei.1
The dwarfs among plant cells are many of the Bacteria,
which have a longitudinal diameter of not quite lyu, (y-^-^mm.).
The petal of a violet consists of about 50,000 cells which are
comparatively large.
By far the greater number of cells have but one nucleus,
and if they are found to contain more than one, it is generally
because the process of cell-multiplication by division is just
beginning. There are, however, some cells that always
contain several nuclei ; such are, for instance, those in the
marrow of vertebrates, and partly also those known as syncytia
in the adipose tissue of insects and other Arthropods.3
In his classical and suggestive work on cell-division among
the Arthropods,3 Carnoy expresses the opinion that these are
all multinuclear giant cells, not masses of cells formed by the
fusion of others. This view cannot be adopted without reserva-
tion, as there are undoubtedly cases in which syncytia arise
from a gradual breaking down of the cell- walls. This takes
place, for instance, in Termitomyia, a sub-genus of Termito-
xenia. In the sub-genus Termitoxenia (in the narrower sense)
1 See Reinke, Einleitung in die iheoretische Biologie, p. 213, and his Mono-
graphie der Gattung Caulerpa. See also Frank, Synopsis der Pftanzenkunde,
III, Hanover, 1886, § 890; van Tieghem, Traite de Botanique (1891), pp. 9, 10.
2 On the subject of syncytia or cell-fusions see also 0. Hertwig, Allgemeine
Biologie (1906), pp. 378-381.
3 ' La Cytodierese chez les Arthropodes ' (La Cellule, I, 1885, n. 2, p. 235, &c.).
54 MODERN BIOLOGY
these adipose cells are very large, but they are distinct one
from the other, though in full-grown physogastric specimens,
in which no further cell- division occurs, there are frequently
two nuclei (cf. fig. 2a) instead of one. According to Weismann1
multinuclear cells occur also in the festooned columns of
cells found in the larvae of flies. I have myself found cells
with two or more nuclei in the halteres of Termitoxenia, and
Bolles Lee discovered them before me in those of common
Diptera.2 In many of the lower orders of plants, such as the
Thallophyta, cells containing several or even many nuclei are
of frequent occurrence, and among the Siphonaceae, a
subdivision of the Algae, there are plants (C aider pa, Vaucheria,
&c.), which consist of one huge multinuclear cell, as has been
already stated.
Just as in the tissues of living organisms there may be, and
actually are, cells which contain several nuclei, but still do
not divide into more cells, so, in the lowest forms of animal
life, tke Protozoa, there are unicellular organisms containing
two or more nuclei, but not forced on that account to split
up into several individuals.
The reader must, however, carefully distinguish the multi-
nuclear cells just mentioned, from others which contain beside
or in the true nucleus one or more little round bodies known
as nucleoli. The founders of cytology, Schleiden and Schwann,
noticed these bodies and regarded them as having some
essential importance in the structure of the cell. This opinion
has proved to be erroneous, and most nucleoli seem to be merely
differentiations of the ordinary substance of the nucleus. For
this reason I have purposely refrained from referring to them
until now, when we are concerned with the more detailed
morphology of the cell.
2. THE STRUCTURE OF THE CELL EXAMINED MORE CLOSELY
In an account of the origin of modern cytology, Gustav
Schlater writes as follows : 3 ' The cell is a little mass of proto-
plasm, endowed with all the properties of life. This was the
1 Die Entwicklung der Dipteren, Leipzig, 1864, p. 132 and Plate 8, fig. 10.
2 ' Les balanciers des Dipteres ' (Eecueil Zoolog. Suisse, II (1885), 389
et pi. XII, fig. 18).
3 G. Schlater, ' Der gegenwartige Stand der Zellenlehre ' (Biolog. Zentral-
blatt, XIX, 1899, Nos. 20-24, p. 667).
STKUCTUKE OF THE CELL 55
definition given by Max Schultze, and at the time our idea of
a cell seemed to have reached its full development. Thence-
forth, we had only to submit cells to examination from many
points of view, and the representatives of every branch of
biology did in fact turn their attention to the cell. The word
"Protoplasm" was ever on their lips, and the number of works
devoted to the examination of the structure and life of this
elementary unit in living substance is so great that it would
be quite impossible for anyone to read them all. This
examination has proved very fertile in results ; every step has
supplied fresh evidence supporting the general biological
importance of the cell-theory ; every book written has proved
that we must start from the cell in order to extend our know-
ledge of nature. The reputation of the cell increased ; it
revealed itself as more and more complex in its formation.
Within it, in this little mass or drop of living substance, modern
research has discovered a complicated structure, and more
and more details of this structure, and each day adds to the
interest taken by men of science in the whole complicated
vital processes that go on in the small compass of the cell.'
The interesting question arises here : Are we to consider
the cell simple or complex ? Is it the ultimate biological
unit in the structure of organisms, or is it itself a diminutive
organism made up of subordinate units ? This is a weighty
question, having an important bearing on the problem of life,
and students are apt to overlook its twofold character. In
order to emphasise it, let us divide the question into two, and
ask : (1) Is the cell morphologically simple ? (2) Is it the
ultimate biological unit of organic life, or is it an aggregation
of lower elementary units ? It is possible to deny the simplicity
of the cell and at the same time to affirm its unity, for, according
to the unchanging laws of thought which are still binding upon
the Homo sapiens of the twentieth century, simplicity and
unity are two quite different ideas. Modern research will
never attain to assured philosophical results regarding the
nature of life, if it confuses unity and simplicity. Let us try
to give to both questions an answer based upon facts.1
1 Cf. 0. Hertwig, Allgemeine Biologic, 1906, chapters ii and iii ; Wilson,
The Cell, 1902 ; Yves Delage, La structure du protoplasma et Us theories sur
rheredite, Paris, 1895.
56 MODEKN BIOLOGY
Is the cell simple ? No, it is not simple, but extremely
complex in many cases, a true microcosm. It consists of a
number of parts that differ morphologically, chemically,1 and
physiologically, and yet on their harmonious connexion
depends the biological unity of the vital process of the cell.
Although all parts of the cell participate more or less in its
vital activities, still the nucleus is of chief importance in the
principal processes.2
Such are briefly the results of the most recent investigations
of cytology, and we have now to consider them more in detail.3
The two chief morphological constituents of the cell are the
cell-body and the nucleus, and this has been universally
acknowledged ever since Leeuwenhoek discovered the nucleus
(see p. 31). At the present time everyone regards them as
essential to the cell, whilst the membranous covering of the
cell and the nucleoli within the nucleus are not essential.4 In
1882 Strasburger suggested the name cytoplasm to designate the
protoplasm of the cell-body, and his suggestion has generally
been adopted.5
It was originally regarded as absolutely homogeneous, but
after Dujardin's study of it (1835) little granules were noticed
in it, and further examination revealed a structure variously
described as filar, reticular, or alveolar. There are many
modern theories regarding the structure of cytoplasm. All
students, with the exception of those mentioned first, agree
in recognising in the protoplasm of the cell-body two distinct
substances, one being transparent and forming the foundation of
1 The chemical constituents of protoplasm and the morphological variety
of the parts of the cell are not discussed here in detail, because very little
is as yet known with certainty about them. (Cf. Chapter II, p. 33.) How
complicated the chemical composition of the nucleus is may be seen on reference
to Dr. Hans Malfatti's work, ' Zur Chemie des Zellkerns ' (BericMe des natur-
wissenschaftlich-medizinischen Vereins, Innsbruck, XX, 1891-2).
2 This fact is acknowledged even by those who, like J. Reinize, regard it
as not essential to differentiate the nucleus as a distinct morphological forma-
tion. (See Reinke's Einhitung in die theoretische Biologie, 1901, p. 256.)
3 An excellent account of the morphology of cells and of the various
theories regarding the structure of the cell-body and the nucleus will be
found in Wilson's The Cell, pp. 19-62.
4 The subject of the centrosomes will be reserved for discussion in Chapter
V. See 0. Hertwig, Allgemeine Biologie, pp. 45-49.
5 0. Hertwig prefers to retain the older meaning of the word protoplasm,
in which it was originally used by von Mohl, Max Schultze and Leydig, to
designate the substance of the cell-body as distinct from the nucleus. Stras-
burger's cytoplasm is thus identical with the protoplasm of these earlier
writers.
STKUCTUKE OF THE CELL 57
the cell (hyaloplasm, as Ley dig calls it), and the other granular,
consisting of microsomes, which form the framework of the filar,
reticular, or alveolar structure (spongioplasm, as Leydig calls
it). The former is also very suitably called cytoplasm, and the
latter cytomitom, but a great number of names have been given
to both,1 names calculated to astound any ancient Hellene who
heard the modern derivatives coined from the wealth of old
Greek words.
Those who believe cytoplasm to be homogeneous do not
recognise the presence in the living cell of two morphologically
distinct substances, but they regard the granules and threads
and meshes of the so-called cell-framework as merely artificial
products, resulting from the chemical reactions and the use
of stains for microscopical purposes.
There are, however, good reasons why this theory does
not find many supporters at the present day,2 for recent micro-
scopical research has revealed in the living cell a structure,
which is not produced by the processes of fixing and stain-
ing, but is only rendered visible by means of them. This is
especially true of the filar structure of spongioplasm, which is
practically identical with the reticular structure or frame-
work. It was discovered first by Karl Frommann in 1875,
but Flemming recognised it as filar,3 and his observations
have been confirmed by those of many other scientists,
such as Klein, Leydig, E. van Beneden, Carnoy, Heidenhain,
Zimmermann, &c., and are now regarded as of unquestioned
accuracy. It is of secondary importance to decide whether, as
Flemming thinks, the protoplasmic threads are of greater
significance, or, in agreement with Klein, Carnoy, &c., we
should lay stress particularly on the network formed by these
threads.
Butschli's alveolar theory represents another view of the
structure of the cell. According to it the protoplasm of the
1 See Biitschli, ' tiber die Struktur des Protoplasmas,' 19 (Verhandl.
der deutschen Zoolog. Gesellsch., 1891, pp. 14-29).
2 A. Fischer, whose theory regarding the polymorphic character of proto-
plasm will be discussed later on, must not be reckoned among those who
uphold the homogeneity of protoplasm.
3 See W. Flemming, ' Uber den gegenwartigen Stand unserer Kenntnisse
und Anschauungen von den Zcllstrukturen,' a paper read at the opening
of the thirteenth meeting of the Anatomical Society at Tubingen on May 22,
1899 (Naturwissenschajtliche Rundschau, XIV, 1899, Nos. 35 and 36).
58 MODEKN BIOLOGY
cell has a structure resembling honeycomb or foam, due to
the mechanical mixture of the various fluid constituents of
protoplasm. That suspended in the fluid hyaloplasm there
are often vacuoles, filled with another kind of fluid, is a fact not
questioned even by the opponents of this theory, but they
deny that the minute structure of the protoplasm depends
merely upon the presence of these vacuoles ; for, whereas
spongioplasm, treated according to Biitschli's methods, ap-
peared to reveal an alveolar structure, closer examination has
shown that a reticular structure really underlies it. The chief
evidence brought forward by Biitschli in support of his alveolar
theory is derived from artificial mixtures of various fluids,
which bear a superficial resemblance to cell-structures, but
cannot of themselves prove anything about the real structure
of the cell.
I have no wish, however, to condemn Biitschli's alveolar
theory, for we ought, in speaking of it, to distinguish between
his view of the honeycomb structure of the cell, and his explana-
tion of that structure by assuming a mechanical mixture of
various fluids. The latter hypothesis is extremely doubtful,
and has been thoroughly discussed by Oskar Hertwig in his
' Allgemeine Biologie ' (p. 23). On the other hand, Biitschli's
theory of the alveolavr structure of many cells has been
strengthened by recent research. In very thin microscopical
sections very highly magnified, what appears as a network
seems in fact often to be only a section'of a framework consisting
not of meshes but of closed chambers ; and, if this is true, in
these particular cells the protoplasm has really not a reticular
but an alveolar structure. In my series of sections of the
large gland-cells in the wing-covers of a termitophile beetle
(Chaetopisfhes Heimi) I have occasionally perceived a distinctly
alveolar structure of the spongioplasm.1 It seems, therefore,
that the alveolar theory may stand beside the reticular theory,
although latterly it has been attacked by those who are
inclined to regard the alveoli seen under the microscope as an
artificial product, or as a pathological vacuolisation of the
protoplasm.3
1 Of. ' Zur naheren Kenntnis des echten Gastverhaltnisses bei den Ameisen-
und Termitengasten ' (Biolog. Zentralblatt, XXIII, 1903, Nos. 2-8, p. 269).
2 Cf. A. Degen, ' Untersuchungen iiber die kontraktile Vakuole nnd Waben-
struktur des Protoplasmas ' (Botanische Zeitung, 1905, Part I, pp. 163-225).
STEUCTUKE OF THE CELL 59
Less satisfactory than Biitschli's alveolar theory is
Altmann's granular theory,1 which is based upon the granular
structure of protoplasm. If Altmann merely asserted that
numerous granules, now generally termed microsomes, are
embedded in the transparent hyaloplasm of the cell, there
would be no objection to his theory, for it would rest on actual
observations. But he goes on to deny the fibrillar or reticular
structure of the spongioplasm, and thinks that it may be
explained as a close series of granules. Flemming, on the
other hand, rightly points out that the microsomes are often
arranged like beads on the reticular' framework, but do not
actually form that framework. Moreover, a large proportion
of Altmann's famous granules have been proved not to be
microsomes at all, but merely artificial products accidentally
resulting from chemical reaction ; in fact, they are metaplasmic
bodies and consist of protoplasm and foreign substances
embedded in it, and were mistaken by Altmann for his granules,
and the scientific value of his theory is greatly diminished in
consequence. Its chief defect, however, is that it regards the
granules contained in protoplasm as alone forming its essential
active basis, and that it boldly accepts them as elementary
organisms out of which the cell, as a secondary formation, is
composed. This view is devoid of all real foundation in facts,
and has been rejected by most scientists. We shall have to
refer to it again later, in discussing the unity of the cell.
There is great diversity of opinion as to the relative im-
portance of the two morphologically distinct constituents of
the cell-body, viz. hyaloplasm (cytoplasm) and spongioplasm
(cytomitom). Heitzmann, van Beneden, Eeinke, Carnoy,
Ballowitz and others agree in thinking the latter, which forms
the framework of the cell, its really living, moving and con-
tractile element, whereas others, and especially Leyden,
ascribe these qualities to the former, and regard the hyaloplasm
as the living substance. As Flemming saw, these two opinions
ought probably to be united, for, as no living cell contains
hyaloplasm exclusively or spongioplasm exclusively, both
must be considered essential constituents of protoplasm,
although most scientists agree with Flemming in assigning
1 Cf. Richard Altmann, Die Elementarorganismen und ihre Beziehungen
zu den Zellen, 1894.
60 MODEEN BIOLOGY
greater importance to spongioplasm than to hyaloplasm. It
is obvious that for the present we must be content to accept
hypotheses of various degrees of probability, and these various
theories regarding the more minute structure of the cell are all
more or less of a hypothetical character.
Quite recently, in 1895-6, another theory as to the
structure of the cell has been brought forward by Friedrich
Beinke and elaborated by Wilhelm Waldeyer, and Gustav
Schlater calls it the newest achievement of modern research
into the morphology of the cell.1 This theory attempts to
reconcile the various views as to the structure of protoplasm.
According to it, in the homogeneous ground-substance of the
cell (i.e. in the cytoplasm, as other writers call it) there is
embedded a reticular framework (cytomitom) ; the formation
of the latter varies, but in the main it is alveolar and in its
walls lie very small granules (microsomes) , which in certain
cases are aggregated, so as to form filaments and network.
The chief framework of 'the cell owes its alveolar structure
to the larger vacuoles and granules which it contains. Keinke-
Waldeyer's theory thus harmonises the views of other scientists,
and we may regard it as summing up all that was known of the
structure of the cell in the year 1900 ; there is, however, one
drawback to it theoretically, for it lays too little stress upon
an essential element, viz. the meshwork or alveolar structure
of the cell-framework, with the rows of microsomes arranged
along it, and it lays comparatively too much stress upon an
unessential element, viz. the vacuoles and larger granules
which the cell contains.
3. THE MINUTE STRUCTURE OF THE NUCLEUS
Hitherto we have discussed only the details of the cell-body,
now we must consider the structure of the nucleus. Here
again we find two chief substances, which, however, differ
morphologically, physiologically, and chemically far more
from one another than do the spongioplasm and the hyaloplasm
of the cell-body. It is often possible to discover in the nucleus
not only two, but three or four protein substances differing
under chemical and microscopical examination. The nucleus is
1 Biolog. Zentralblatt, XIX, 1899, No. 20, p. 676.
STKUCTUKE OF THE NUCLEUS 61
therefore, as 0. Hertwig rightly remarks, a very complex l
formation, so far as its constituents are concerned. According
to their behaviour when stains are applied to them to facilitate
their microscopical examination, the two chief substances in
the nucleus have been called chromatin and achromatin ;
according to their chemical properties they are called nuclein
and linin respectively. Chromatin or nuclein takes a brilliant
colour when treated with carmine, haematoxylin, &c., whereas
achromatin or linin is either not stained at all or takes a colour
only under special circumstances. Achromatin resembles
in structure the protoplasm of the cell-body, for it contains
a fluid known as karyoplasm, and a fibrillar or reticular or
alveolar framework known as karyomitom. These are analogous
to the cytoplasm and cytomitom of the cell-body. Large nuclei
are bounded on the outside by a peculiar nuclear membrane.
Chromatin has been mentioned as one of the chief substances
in the nucleus ; the parts that are readily stained are formed
of it, and it is composed of nuclein.2
Closely connected with it, though differing chemically
both from chromatin and from achromatin or linin, is another
substance, less readily stained, known as plastin or paranuclein.
Nuclein and plastin together form the chromatin nucleoli, the
chromatin nuclear framework, or the chromatin skein-like
nuclear filaments ; these are only different names for the
different forms assumed by the nuclein-plastin elements in the
nucleus.
With regard to the relation in which they stand to the
achromatic nuclear framework, many theories have been pro-
pounded by Memming, Carnoy and others, but we cannot
discuss them in detail now. For the present let it suffice to
say that two distinct kinds of nucleoli have been discovered, the
one kind very readily stained, the other less so, but both con-
sisting of combinations in different proportions of nuclein
and paranuclein, whilst on the other hand the true nucleoli or
plasmosomes are not susceptible to any stain, consist only of
paranuclein (pyrenin), and form more or less transparent
vacuoles.
1 Allgemeine Biologie, p. 29. For further details as to the constituents
of the nucleus, see pp. 29-44.
2 Cf. J. Reinke, Philosophic der Botanik, 1903, pp. 69 and 72.
62 MODEKN BIOLOGY
It may be asked why different parts of the cell behave in
such different fashions, when the same stain is applied to them,
and so render it possible for us to penetrate into the mysteries
of its structure. Two theories have been put forward to
account for this behaviour. According to one, which is known
as the chemical theory of stains, it is assumed that the degree
of readiness with which the various parts of the cell take a
stain depends upon the amount of chemical affinity existing
between the various albuminous compounds and the stain
applied. According to the other and newer theory, certain
parts of the cell are susceptible to stain, only because of the
changing physical qualities of the thing stained, and, as a
result, its powers of absorption vary. Alfred Fischer is the
chief supporter of this physical theory.1 It seems probable
that both theories are more or less true, and that the staining
capacity of the various morphological elements of the cell
may be ascribed partly to chemical and partly to physical
causes.
In close connexion with his examination of the effects of
fixing and staining upon the substance of a living cell, A.
Fischer has propounded a new theory, which he designates
that of the polymorphism or pleomorphism of protoplasm.3
He believes protoplasm to be in general viscous, containing
structures of various shapes, granular or reticular, some of
which remain permanently, whilst others are of a transitory
nature. All these varieties in the cell-framework are due to
definite albuminous compounds fluctuating between a fluid
and a solid condition. Moreover, Fischer is of opinion that
protoplasm is often homogeneous on the surface, but in the
interior occur granules, filaments, reticular framework, and
occasionally also Butschli's alveolar structures. Fischer is
not a supporter of the absolute homogeneity of protoplasm,
for in the face of ascertained facts this can no longer be defended,
but he admits that the various cellular structures observed by
modern scientists are, at least to a great extent, not artificial
products, i.e. the results of staining and fixing, but occur
also in the living cell. He does not, however, believe that
1 Fixierung, Farlung und Ban des Protoplasmas, Jena, 1899.
2 We find similar ideas in Yves Delage's La structure du protoplasma et
les theories sur Vheredite, pp. 30 and 31.
MOKPHOLOGY OF THE CELL 63
these structures point to any chemical difference in the parts
of the cell, but are the outcome of the physical conditions
affecting the protoplasm at any given moment. Fischer
obviously does not intend to deny the complex chemical com-
position of living substance, but he doubts whether there is
any necessary connexion between the chemical constitution of
the parts of the cell and their staining capacity — such a con-
nexion as would justify our assuming that a chemical difference
exists between parts that show a different staining capacity.
Although Fischer's theory of the polymorphism of proto-
plasm has a good deal that is hypothetical about it, there is
far more actual foundation for it than for Altmann's granular
theory ; in fact, the latter bears the character of a phylogenetic
speculation rather than that of a scientific theory. The theory
of the polymorphism of protoplasm has one great advantage,
viz. that it reconciles the conflicting opinions regarding the
morphological structure of the cell with one another, and
supplies one uniform explanation of the actual variety of
phenomena.
4. SURVEY OF THE HISTORICAL DEVELOPMENT OF THE
MORPHOLOGY OF THE CELL
What, then, is the morphology of the cell in the light of
modern research ? This question can be answered best, if
we glance back at the views regarding the structure of the
cell that have been~ current at various stages of cytological
research. They may be represented by the diagram on p. 64
(figs. 3-6).i
Fig. 3 is a cell as Malpighi (1678) and Wolff (1759) conceived
it ; it consists simply of the enclosing membrane, and so is
nothing but an empty sac.
Fig. 4 is a cell such as Schleiden and Schwann described
(1838-9). The membrane is still an essential part, but it is
now partly filled with fluid, in which is suspended another
essential part, viz. the nucleus, with one nucleolus.
Fig. 5 is the cell according to Ley dig (1857) and Max
Schultze (1861). The viscous fluid fills the whole sac, and
1 Cf. M. Duval, Precis d' Histologie, 1900, pp. 25, 31. Also G. Schlater, 'Der
gegenwartige Stand der Zellenlehre ' (Biolog. Zentralblatt, XIX, 1899, p. 756).
64
MODEKN BIOLOGY
surrounds the nucleus and its nucleolus, but the membrane
has disappeared as not essential to the existence of the cell.
Subsequently the finer structure of the cell was more closely
examined, and the mass of apparently homogeneous proto-
plasm was seen to be a compound formation, consisting of
framework and fluid, whilst the nucleus, too, was found to
contain, besides the nucleolus, an achromatic framework
embedded in nuclear fluid, and also a chromatin framework
that assumes various forms. We may connect the names of
FIG. 3.
FIG. 4.
FIG. 5.
FIG. 6.
Schlater, Keinke, and Waldeyer with this stage of cellular
morphology (1894-5).
Fig. 6 represents it according to Carnoy,1 who regards the
cellular framework as reticular, and the chromatin nuclear
framework as consisting of a coil of nuclein-plastin thread.3
This conception of the cell harmonises best with my own
cytological examination of the huge pericardial 3 cells of the
Termitoxenia (Termitomyia) mirabilis.
1 Carney's valuable work in the development of cytology has been already
mentioned. See p. 46.
2 Cf. also E. B. Wilson, The Cell, p. 35. Fig. 13A is an admirable representa-
tion of a permanent spireme nucleus, showing chromatin in a single thread
(Balbiani).
3 This is the name given to some peculiar cells, allied to the adipose cells,
and connected with the ' heart ' of the insect, i.e. with its vas dorsale.
MOKPHOLOGY OF THE CELL 65
Within the chromatin thread of the nuclear framework it
is possible in many cases to perceive a still finer morphological
differentiation. In the American salamander Batrachoseps
the threads are plainly divided and each pronucleus contains,
according to Gustav Eisen, twelve chief parts or chromosomes. l
Each chromosome as a rule is subdivided into six chromomeres,
in each of which on an average six of the most diminutive
bodies or chromioles can be traced. There are therefore about
400 distinguishable parts in the chromatin thread of the nucleus !
There are also other animal and vegetable cells, which, before
division, show only a coil of chromatin thread, or a chromatin
framework, but, in the course of indirect or mitotic division, this
develops into definite groups of chromatin knots or chromo-
somes ; whilst within the achromatic framework, that was
previously scarcely visible, there now appear as organs of cell-
division tiny round centrosomes, in the midst of which rises an
achromatic spindle. All these phenomena will be discussed
more fully in Chapters V and VI, for they do not properly
belong to the morphology of the resting cell, or cell not in
process of division.
The cell is therefore far from being a simple formation ;
it is, on the contrary, composed of parts differing widely from
one another, and having different functions in its life. We
have now to consider the chief kinds of activity in the cell,
and the parts taken in this activity by the morphologically
different elements of it, and then we shall be in a position to
discuss the question whether the cell is the ultimate unit in
organic life, or whether it is equivalent to an aggregate of still
more simple and elementary units. A result of this discussion
will be to show us what ought to be our attitude, as students of
natural science, towards the famous theory of the spontaneous
generation of organic beings.
1 Pronucleus is the name given to the nucleus of both the egg- and sperm-
cells immediately after their union in the process of fertilisation. See
Chapter VI.
CHAPTER IV
CELLULAR LIFE
1. THE LIVING ORGANISM AS A CELL OR AN AGGREGATION OF CELLS.
Division of labour among cells (/;. 68). Life a process of movement
directed to a material end (p. 69).
2. ACTIVITY OF LIVING PROTOPLASM.
Phenomena of movement in Amoebae and other Rhizopods (p. 70).
Life and work of the white blood-corpuscles (leucocytes) (p. 72).
3. EXTERIOR AND INTERIOR PRODUCTS OF THE CELL.
Cilia and flagella as external organs of movement belonging to the cell
(p. 74). Interior products of the cell. Various biochemical
departments of work. Biological importance of fat and of
haemoglobin (p. 75).
4. THE PREDOMINANCE OF THE NUCLEUS IN THE VITAL ACTIVITIES OF THE
CELL.
Vivisection of unicellular animals and plants (p. 80). The nucleus the
central point of the vital processes in the cell (p. 83).
1. THE LIVING ORGANISM AS A CELL OR AN AGGREGATION
OF CELLS
CELLS are the bricks composing the whole building of the
organic world. Therefore to them also is the Creator's com-
mand addressed : ' Increase and multiply/ for without growth
and multiplication of cells no organic life is conceivable. All
living creatures consist of one or more cells ; if they are uni-
cellular, increase is possible only if from one cell several cells
are formed ; if they are multicellular, growth and increase
are possible only by way of growth and increase of the cells
composing their organs and tissues.
In the previous chapter we discussed the structure of the
resting cell, as revealed to us by modern microscopical research ;
we have now to turn our attention to the cell as active and
alive. In the case of unicellular animals and plants, the
diminutive mass of protoplasm with its one nucleus is the one
organ that has to discharge all the functions of life ; it is,
to compare small with great, a Jack-of-all trades in the economy
of life. Nutrition and multiplication, as well as independent
movement and sensation (as far as these latter manifest them-
66
CELLULAR LIFE 67
selves in unicellular creatures), all depend upon one and the
same atom of living substance. It is true that here, in spite
of the diminutive size of the creature under consideration,
we have something analogous to what is called ' organisation ' in
higher animals, for, as we shall show later on, the morphologi-
cally different parts of the cell have various functions. Still,
strictly speaking, the parts of the cell ought not to be called
organs, although, perhaps, we may follow some recent writers
and call them organellae, at least when speaking of the multi-
cellular animals known as metazoa. In their case, whenever
we use the word organ, we mean some part consisting of definite
tissues and serving as an instrument in the vital activity of an
individual. As the tissues are made up of cells, which are
therefore the ultimate constituents of the organs, it would be
logically wrong to apply the same word ' organs ' to the smallest
parts of the cells themselves. It has lately become too much
the custom to disregard the connecting membrane which unites
cells together to form tissues, and tissues to form organs. The
result of this has been that, in both the higher animals and plants,
the cell has come to be regarded as having an independent
existence, as being an individual of a lower order. This view is,
however, altogether mistaken, and it is no less wrong to apply
the name ' organs ' to the minute constituents of the cell,
which differ morphologically and physiologically. If they are
organs at all, they are so only in a loose, metaphorical sense.
It is only in the case of unicellular organisms that this
theoretical opinion corresponds with facts, for in them the
constituent parts of the cell really discharge the vital functions
of the individual, and so are equivalent to the organs of multi-
cellular organisms. For this reason the unicellular organisms
form the lowest rung of the ladder of organic perfection. The
higher we ascend, the more are the various parts differentiated
to perform distinct functions, and the greater is the perfection
of the organisation. A vertebrate animal, or even a tiny
insect, is a well-ordered and regulated state, whose inhabitants
and officials are thousands and tens of thousands of cells.1
1 The reader must notice that this expression is figurative. In reality,
as has been already pointed out, the cells of a multicellular organism are not
individuals, because they are not physiological units complete in themselves,
as are unicellular organisms. On this subject see Chapter VII, § 1 : ' The cell
as the ultimate unit in organic life.' Cf. also 0. Hertwig, Allgemeine Biologic,
1906, chapters 14-17.
F 2
68 MODEEN BIOLOGY
All are democrats, for none is of higher origin than the
others ; the nerve-cell of the brain, which exercises control,
like the ruler of the state, is a cell in exactly the same way
as the glandular cell of the stomach, or the epithelial cell
of the skin. But in spite of their genuinely democratic disposi-
tion, the cells are by no means anarchists ; there prevails
among them a most perfect harmony, based upon a regular
division of labour between the various organs, tissues, and
cells.1
Just as in every well-ordered state different duties are
assigned to different officials, so to various organs are assigned
the functions of nutrition, digestion, circulation of the blood,
respiration, propagation, movement and all the work done by
the nerves and senses. But these organs, which resemble the
heads of departments in the state, are themselves made up
of different kinds of subordinate tissues, and each tissue con-
sists of a more or less varied combination of cells, differing
in the case of the different tissues. All these millions of cells
compose what we call an organism, and in spite of their vast
number and endless variety they all have the same origin,
for they all proceed from an egg-cell fertilised by means of a
spermatozoon ; such at least is the ordinary process of develop-
ment of any higher organism.2
The continuation of the process of cleavage, begun in the
first cleavage or segmentation nucleus, leads eventually to a
differentiation of the living creature into various cells, tissues
and organs, until it attains its full development, and then
the work of propagation renews the cycle of life. But even
the egg-cells and the spermatozoa, although they carry on the
task of propagation, differ in no respect from other cells, as far
as their origin is concerned ; in the course of embryonic
development they are differentiated from common cells,
into which the fertilised egg split up at the formation of the
periphery of the embryo.3
1 On the subject of the division of labour in an aggregation of cells, see
0. Hertwig, chapter 17, pp. 417, &c.
2 I sayy ordinary,' because of the phenomena of parthenogenesis among
insects, &c., where the egg-cell develops without fertilisation. (See Chapter
VI, §6.)
3 See Chapter VI, § 3, for the most recent results of investigations regarding
the distinction between somatic and germ cells, which is either very early
or even original.
CELLULAR LIFE 69
All the cells, therefore, in the organism enjoy absolute
' equality before the law,' but it is an equality, not of death
but of active life, inasmuch as from cells, at first similar, the
mysterious laws of organic development produce the living
being in all its wonderful, complete, and complex structure.
Such is in outline the cellular life of the multicellular
organism, which we cannot now discuss in greater detail.
What has been said will suffice to show that the cell must be
called the lowest unit of organic life in multicellular animals
and plants. Let us now study more closely the vital processes
affecting cells as such, whether they are united to form tissues
of a higher order, or lead an independent existence as unicellular
beings. This study will give us a deeper insight into the real
nature of the cell, this marvel of creation.
Life is, in its physiological aspect,1 an uninterrupted
process of movement, every phase of which tends to the pre-
servation of the individual and of the species. The interior
movements, which form the really essential processes of
vegetative life, tend to the assimilation of fresh material, and
so to the growth of the individual. These processes of assimila-
tion, depending as they do upon nutrition and respiration, are
necessarily closely connected with analogous phenomena of
dissimilation,3 for the building up of what is new requires a
tearing down of what is old, and the reception of fresh nutritive
matter and its transformation into living substance necessitate
a removal of what is worn out. Growth is based upon assimila-
tion and leads naturally to numerical increase. As soon as a
cell has reached a definite maximum size, it divides and forms
new cells ; if these remain united in one aggregate of tissues,
the division of the cell promotes the growth of the individual ;
if, however, the new cells separate from the parent organism,
so as to form new independent individuals, then the division
of the cell is a process of propagation, and furthers the
preservation of the species. To these interior processes of
movement in the living substance correspond other exterior
1 For further details regarding the physiology of the vital processes, the
nutrition and transmutation of energy of cells, and the processes of assimi-
lation and dissimilation, see Bunge, Physiologische Chemie, and J. Reinke,
Einleitung in die theoretische Biologic, chapters 26-29.
- The word dissim lation was introduced by Hering as an euphonious abbre-
viation of des-assimilation, which, being a clumsy word, is now but little used.
70 MODEEN BIOLOGY
movements, due to the susceptibility of protoplasm to definite
external stimuli ; these latter movements tend to procure the
material necessary to support the interior vital processes,
whether it be by the assimilation of food to promote individual
growth, or by the union of individuals to promote the preserva-
tion of the species ; finally, the exterior movements protect
the organism from its enemies. Thus all the exterior move-
ments are subservient to the interior, even when, as voluntary,
they belong to conscious existence, and therefore are on a higher
level than the vegetative processes, for the whole conscious
life of an animal aims at the preservation of the individual
and of the species ; it stands to living matter in the position
of a slave ; its sole aim is material, and it has no power to rise
above the material, as the intellectual life of man enables him
to do.
2. ACTIVITY OF LIVING PROTOPLASM
The foregoing general observations will enable us to under-
stand the phenomena that we are now about to consider.
Oskar Hertwig in his ' Allgemeine Biologie,' pp. 108, &c.,
recognises several distinct kinds of movement in protoplasm,
and we may safely follow him on this point, Keal protoplasmic
movement either belongs to a complete protoplasmic body,
such as an amoeba, or it takes place in the interior of a cellular
membrane. This latter form of movement occurs chiefly in
plants, and is divided into rotatory and circulatory move-
ments. The rotatory movement was discovered by Bona-
ventura Corti as early as 1774. We must distinguish these
genuine movements of protoplasm from those due to exterior
appendages on the cells, such as cilia and flagella, with which
we shall deal in the next section of this chapter. We must
refer also to the movements of pulsating vacuoles in unicellular
animals, and to the manifold passive alterations in shape and
position undergone by the cells of an organism in consequence
of the vital process going on within it as a whole. At present,
however, we are concerned only with a few instances of true
protoplasmic movement.
The protoplasm of a living cell is in a state of constant
activity, and moves on definite lines inside the cell, its course
PEOTOPLASMIC ACTIVITY 71
being apparently determined by the framework of spongio-
plasm. At the end of the eighteenth and at the beginning of
the nineteenth century Corti and Treviranus noticed (see p. 33)
that the chlorophyll granules, which give plants their green
colour, are frequently in vigorous movement within the cells ;
later on, in 1848, von Mohl discovered this granular movement
not to be active, but passive, and due to the power of contrac-
tion possessed by protoplasm. In many of the lower animals
protoplasm appears capable of active movement, but we must
be careful to distinguish two forms of activity — the active
movement of the protoplasm framework, that manifests itself
especially in external changes of shape, and a more passive
flow of the granules in the cell-sap, which is a result of the
contraction and expansion of the protoplasmic framework. It
is obvious that these processes of movement cannot always
and everywhere be traced with the same clearness in living
cells. They can be seen very well in various little unicellular
creatures possessing no enclosing membrane, such as the
Amoeba proteus,1 and still better in other animals belonging to
the same class of Khizopods, but having a thin shell, through
the openings of which the so-called pseudopodia protrude, as,
for instance, in the case of the Gromia oviformis.*
The body of the Amoeba is subject to constant changes
of shape, whence the creature has received its name. It can
protrude protoplasmic continuations of its substance in all
directions and again withdraw them. The pseudopodia are
outstretched to catch food and to effect a change of place ;
they are withdrawn when any danger threatens. If the
pseudopodia of an Amoeba are fed with very small grains of
carmine, these grains are at once surrounded by the proto-
plasm of the pseudopodia and absorbed by it, and then they
share in the interior flow of the protoplasm and render it
visible under the microscope. In Amoebae there is no
sharp distinction between interior and exterior movements,
for both are nothing but the same flow of the same protoplasm.
When the pseudopodia discover anything edible they close
round it, and it at once becomes the centre of a vortex of
1 The changes of shape undergone by this little Amoeba were described
as early as 1755 by Roesel von Rosenhof.
2 Within the pseudopodia of true Amoebae no movements can be dis-
cerned, although they occur in the other Rhizopods.
72 MODEEN BIOLOGY
protoplasm, for the creature's whole body contracts round its
prey. The same protoplasm, which sought and captured its
food, now proceeds to assimilate it, and digests as much of it
as is digestible, and then rejects the rest by uncoiling the
enclosing ring of protoplasm.
More vigorous movements than those of the Amoeba can
be observed, as already stated, in the pseudopodia of many
other Khizopods, especially the Foraminifera and Eadiolaria,
which possess a solid skeleton of chalk or silica, and through
its openings protrude the long pseudopodia in quest of food or
to effect change of place.
Amoeboid movements as well as the granular flow of proto-
plasm may be produced, checked, and altered by mechanical,
chemical and thermal stimuli, and this constitutes the chief
proof of the irritability of living protoplasm.
Analogous to the action of the Amoebae and their relations
in the wrater is that of some cells in the organism of multi-
cellular animals, especially of the white blood-corpuscles or
leucocytes. They too possess amoeboid prolongations, enabling
them to move and traverse all the tissues of the body. In order
to pass through a narrow crevice, they put out a pseudopodium
first, and gradually the whole body of the cell follows it.
Cohnheim, who discovered the power of the leucocytes to
wander through the tissues of the body, bestowed upon it the
very suitable name of Diapedesis. These wandering cells have
an almost insatiable appetite ; they are like tramps, always
hungry and thirsty, and they attack other cells, as well as
any extraneous substances that have penetrated into the body,
and encounter them on their way. The leucocytes surround
these on all sides and devour them, hence their other name
of Phagocytes. Their voracity gives them a high degree of
importance in the life of the organism. The white blood-
corpuscles discover the red blood-corpuscles that are old and
incapable of taking up oxygen, and seize them and carry them
off, and thus, by consuming the useless members of the com-
munity of cells, the leucocytes are able to impart the nourish-
ment so obtained to other active formative elements of the
body. They are the police, appointed to keep order in the
cell-republic that we call an organism. They go to and fro
through all the tissues and purify them from hostile bacilli
LEUCOCYTES 73
and other wrongdoers. Whenever they light upon anything
harmful, they simply close round it and devour it ; or, if it is
altogether inedible, e.g. a speck of coal dust, they arrest it and
drive it over the frontier. The leucocytes are therefore real
sanitary inspectors in the organisms of man and the higher
animals. Many authors ascribe to their agency the assimilation
of the nutritive matter absorbed in the intestinal glands, as
well as the diffusion of nourishing lymph throughout the
whole body,1 and from this point of view the wandering
leucocytes appear as nurses, supplying food to the other cells
and tissues. On the other hand, however, under certain
morbid conditions, leucocytes increase with such overpower-
ing rapidity as to become dangerous. They then attack
cells that ought to be left in peace, and so excite a kind of
revolution resulting in inflammation and suppuration of the
tissues, and tending to the eventual destruction of the whole
organism. In spite, therefore, of their physiological merits,
leucocytes have acquired a bad reputation in cellular
pathology. Moreover, the most recent investigations carried
on by Ehrlich, Metchnikoff and others have deprived
leucocytes of many of the police functions generally ascribed
to them. According to the most modern views, the struggle
between health and disease is fought out chiefly by toxins and
antitoxins, the former being chemical substances injurious to
the organism, and given off by harmful bacteria, &c., whilst
the latter are the chemical antidotes, produced by the organism
itself as a protection against toxins. Modern processes of
inoculation aim at causing immunity from certain diseases by
producing specific antitoxins.
A harmless counterpart to the pathological action of
leucocytes in the bodies of men and the higher animals occurs
in the phagocytes of those insects which undergo a complete
metamorphosis. To these cells is assigned the pleasing task
of devouring the old tissues of the larval body during the pupal
stage, in order to impart the stored-up nutritive matter to
other cells concerned in the formation of the new tissues of the
imago.
A flow of protoplasm occurs also in cells where it has
deposited an exterior membrane and cannot therefore protrude
1 Cf. M. Duval, Precis d'Histologie (1900), p. 42.
74 MODEKN BIOLOGY
pseudopodia, but in this case the movements are limited to
the interior of the cell. This movement of protoplasm in
plant cells has long been known to botanists and often described,
for instance, in the leaf cells of the Elodea canadensis and in
the stamens of the Tradescantia, &c.
3. EXTEKIOR AND INTERIOR PRODUCTS OF THE CELL l
Just as the activity of the protoplasm inside a cell enables
it to form a solid membrane as its envelope, so it can produce
movable processes on the surface of the cell, such as cilia and
flagella, which facilitate the locomotion of the cell. In this way
ciliated and flagelliform cells arise. The latter have either
one or a few long, thick processes, whilst the former have rows
of delicate hair-like threads. Among the Infusoria there is a
class of unicellular creatures called Flagellata, from their
having these flagelliform processes, and another class of
Protozoa is known as Ciliata, because their cell-walls are
provided with cilia, which enable them to move about in the
water. Cilia are important in the ingestion of food, for
these creatures, though unicellular and of diminutive size,
have voracious appetites. The ring of cilia surrounding the
oral aperture of an infusorian by its rhythmical motion produces
a vortex in the water, at the centre of which is the mouth of
the little animal. If a tiny diatom or another of the Algae
is caught in this vortex, it has no chance of escape ; it is sucked
down and vanishes in this Scylla, and only its indigestible
remains are eventually thrown up.
Flagelliform and ciliated cells occur also in multicellular
animals. Spermatozoa are simple flagelliform cells, of which
the nucleus forms the head, and a long thread of protoplasm
the body and tail. Ciliated cells occur chiefly in the respiratory
and digestive apparatus, and in this case the cilia do not assist
in the movement of the cell to which they are attached, but
in that of the substance passing over them. The cilia of the
trachea serve to expel small foreign bodies that have entered
the respiratory orifices, and those of the oesophagus help to
carry down the nutritive fluids taken in through the mouth,
and to keep them in steady movement towards the digestive
1 See 0. Hertwig, Allgemeine Biologie, 1906, pp. 79, &c., pp. 100, &c.
EXTEEIOK AND INTEKIOK CELL PKODUCTS 75
organs. In many of the higher and lower animals ciliated
cells occur in the real digestive canal. I have seen very
beautiful ones, magnified 1500 times, in the transverse sections
of the mesenteron of the Termitoxenia (Termitomyia) Braunsi.
The outward or exoplasmic products of the cell are the
external results of the internal activity of the protoplasm.
They may take the form of a cellular membrane, whether it is
homogeneous with the protoplasm (as is the case with most
animal cellular membranes), or whether it is a chemical product
of protoplasm, as is the case with the cellulose cell-walls of
plants,1 or the shells of many of the lower animals (e.g. the
Foraminifera) or the coverings of plants (e.g. the Diatomaceae)
which have been hardened by taking up silicic acid or carbonate
of lime. Further exoplasmic products of the cell are the
elastic intercellular bridges uniting cells with one another,
arid the cilia and flagella which pro trade from the cellular
membrane.
The internal or endoplasmic products of the cell are
contained in its interior. They are of most frequent occurrence
in the vegetable kingdom. In the chemical laboratory of the
living plant cell grains of starch are being prepared which
supply the world with sugar, either directly, or indirectly
through the activity of the plant. Starch is the form in which
the plant stores up~ the carbo-hydrates that produce sugar.
The protoplasm of plants was believed to form chlorophyll
under the influence of light, thus giving its colour to the foliage ; 3
but recently many scientists have inclined to the opinion that
chlorophyll is not a cellular product, and that its presence, not
only in many lower animals, such as the Hydra viridis, but
also in plants, is due to a symbiosis of special chlorophyll
cells with other vegetable or animal cells.3
1 The young membrane of a plant cell consists alwa}^ of cellulose, but
in many instances the cell- walls harden later on into cork or wood.
2 The granules which convey the colouring matter originate in the plant cell
even without the influence of light, although the green colour, which can
be extracted from them, only develops as a rule when light is admitted. Young
fir trees are green, however, and full of chlorophyll, even when grown in the
dark, and several cryptogams become green in spite of complete exclusion of light.
3 Cf . G. Mereschkowsky, ' Uber Natur und Ursprung der Chromatophoren
im Pflanzenreiche ' (Biolog. Zentralblatt, XXV (1905), No. 18, pp. 593-604).
He believes the Cyanophyceae to be independent chromatophores, and tries
to account for the origin of the vegetable kingdom, and its difference from
the animal kingdom, by assuming that they have penetrated into animal
cells. In fact a lion, sleeping under a palm tree, would change places with it,
76 MODEEN BIOLOGY
Animal and vegetable fat is a product of the interior
activity of the cell, and is stored up in its empty spaces. In
the animal kingdom this biochemical branch of industry is of
great importance, and a special class of fat-forming cells,
called adipose cells, often make up large quantities of tissue.
In their vacuoles little drops of fat collect and grow, until
finally the whole cell resembles a ball of fat surrounded by a
membrane. The neighbouring cells that are not of this class
can feed upon this stored-up fat by way of endosmosis. The
protoplasmic product that we call fat is of great importance in
the nutrition of the animal organism. It used to be regarded
as the material for supplying heat in the process of combustion
connected with respiration. In insects fat is closely connected
with the formation of blood, for which reason, in speaking of
them, we often call the adipose tissue simply the blood-forming
tissue. I found many instances of this connexion between
fat and blood in the course of my microscopical study of the
inquilines among ants and termites, and especially in the
physogastric guests of the termites, which rejoice in an extra-
ordinary abundance of fat. In the larvae of the termitophile
beetle of Ceylon, known as Orthogonius Schaumi, the outer
edge of the huge adipose tissue may be seen just at the spot
where it touches the hypodermal masses of blood, and it is
frequently in a state of disintegration, and being absorbed
almost imperceptibly by the diminutive corpuscles of the
insect's blood. I observed similar phenomena in other genuine
inquilines among the termites, which become physogastric
through their abundance of adipose tissue ; the same transition
from adipose to blood tissue appeared on a series of sections
of a termitophile insect, Xenogaster inflata of Brazil. The
ants and termites seem to appreciate the advantages of their
guests' adipose tissue, and hold to the dictum Omne pingue
bonum ; for all their true inquilines, belonging to the class
of beetles, possess a great deal of fat, and it is this tissue
which directly or indirectly emits the volatile exudation that
attracts them so greatly and induces them to lick their guests.1
provided the cells in his body were filled with chromatophores (p. 604). This
is certainly a very hold theory.
1 Cf. on this subject ' Zur naheren Kenntnis des echten Gastverhaltnisses
bei den Ameisengasten und Termitengasten ' (Biolog. Zentralblatt, XXIIT,
1903, Nos. 2, 5, 6, 7 and 8, p. 68).
INTEKIOK CELL PKODUCTS 77
There are a number of other products of the interior of
the cell which might be mentioned ; some of them occur in
animal cells and some in vegetable, and take the form of
essential oils, colouring matters, nectar, caoutchouc and
india-rubber, resin, tannic acid, poisons of various kinds,
digestive ferments, &c., thus serving the most manifold and
interesting biological purposes.
In vertebrate animals the haemoglobin of the red blood-
corpuscles is one of the products of the interior of the cell.
This haemoglobin, to which blood owes its colour, carries the
life-giving oxygen which we breathe in ; the molecules of
oxygen are brought through the lungs into the blood, and
accompany the red blood-corpuscles over the whole extent of
the arterial circulation, making their way through the finest
capillary vessels to the single cells of the tissues, where they
give out their oxygen and so oxydise the existing organic
connexions. The free carbonic acid, which is the chief
combustion product of the vital process, has now to be expelled
from the body by the same means ; so the red blood-corpuscles
are accompanied by carbonic acid molecules on their way
back from the capillary vessels, through the whole extent of
the venous circulation, until they reach the lungs, where
the carbonic acid is breathed out into the air, and at the next
inspiration fresh oxygen is taken up, to join the red blood-
corpuscles on their next journey through the body. The
arterial and the venous blood differ in colour because the
haemoglobin of the red blood-corpuscles forms a soluble
chemical combination with the oxygen, producing bright
red oxyhaemoglobin, whilst the same blood-corpuscles, after
giving off their oxygen to the cells of the body, resume their
previous dark bluish-red tint.
4. THE PKEDOMINANCE OF THE NUCLEUS IN THE
VITAL ACTIVITIES OF THE CELL
We have now considered some characteristic instances of
the processes of cell-nutrition, cell-growth, and cell-motion.
Before passing on to a new and important class of phenomena
of cellular life, viz. the process of multiplication by cell-division,
we must examine more closely the part played by the nucleus
78 MODEEN BIOLOGY
in the manifestations of cell life already described.1 We have
to answer this question: Are the nutrition and growth of
the cell and the formation of its interior and exterior proto-
plasmic products to be ascribed to the cell-body, or does the
nucleus participate in them as an essential element ?
B. Hertwig says, in his ' Lehrbuch der Zoologie,' 7th ed.
p. 55 (Eng. trans, p. 67), that 'for a long time the functional sig-
nificance of the nucleus in the cell was shrouded in complete
darkness, so that it began to be regarded, in comparison with
the protoplasm, as a thing of little importance.' In fact, a
merely superficial consideration of the phenomena already
described might easily lead us to doubt any participation in
them on the part of the nucleus. If, for instance, a little
Amoeba grasps its still smaller prey with its pseudopodia
and devours it, we can observe a series of movements
about and in the viscous protoplasm of the creature's body,
but we can perceive no change in its nucleus. If, on the other
hand, a plant cell is trying to thicken a definite portion of its
enclosing membrane by depositing layers of cellulose, the
nucleus may be seen to quit its former position in the centre
of the cell, and to approach that part of the periphery where
the depositing action of the protoplasm is at its height, and,
when the task is accomplished, the nucleus comes back to the
middle of the cell. In the same way the nuclei of certain
unicellular plant-hairs approach the offshoot as long as it is
in process of formation, but when its growth is complete they
return to their original place. The eggs of the threadworm
(Rhabdonema nigrovenosum) have been observed during the
process of cleavage, and the nuclei of the newly formed cells
moved towards the surface of the cell, where the fresh mem-
brane was forming, and after remaining there for some time, on
the completion of its formation, they withdrew into the centre
of the cells.3
1 Cf. on this subject especially 0. Hertwig, Allgemeine Biologic. (1906),
chap. 10, pp. 249, &c.
2 Cf. L. Rhumbler, ' Uber ein eigentumliches periodisches Aufsteigen
des Kerns an die Zelloberflache innerhalb der Blastomeren gewisser Nematoden'
(Anatomischer Anzeiger, XIX, 1901, pp. 60-88). See also the address delivered
by the same scientist at the seventy-sixth assembly of German naturalists at
Breslau, on September 23, 1904, and printed under the title ' Zellenmechanik
und Zellenleben ' in the Naturwissenschaftliche Rundschau, 1904, Nos. 42 and
43. See especially pp. 546 and 548.
IMPOKTANCE OF THE NUCLEUS 79
Numerous similar phenomena, pointing to a participa-
tion of the nucleus in the processes of nutrition and forma-
tion, were described in 1887 by Haberlandt, an eminent
botanist,1 and in 1889 by Korschelt, a zoologist.2 These two
scientists deduced the following conclusions from their
observations : —
1. The fact that the nucleus occupies a definite position
only, as a rule, in a young cell in course of development
suggests that its functions are connected primarily
with the processes of cell-development.
2. From its position we may assume that the nucleus is
especially concerned, during the growth of the cell,
with the thickening and spreading of the cellular
membrane ; but it is quite possible that in a
fully grown cell the nucleus has other functions to
discharge.
3. The nucleus is concerned not only with the cell's power
of secretion, but also with its nutrition. We can
infer this both from its position and also from
the fact that it sends out numerous branches, thus
increasing its surface on the side nearest to the place
where secretion or nutrition is going on.3
We must refer here also to the correlation between the
size of the protoplasmic body and that of its nucleus, which
E. Hertwig calls the Kernplasmar elation. ^ It can be explained
by the interior reciprocal action of the cell-body and cell-
nucleus. What actual observation pronounced probable has
been confirmed by experiments. Gruber, Nussbaum, B. Hofer,
Verworn, Balbiani, Lillie, Klebs and others had recourse to
1 ' t)ber die Beziehungen zwischen Funktion und Lage des Zellkerns bei
den Pflanzen,' Jena, 1887.
2 ' Beitrage zur Morphologie und Physiologic des Zellkerns ' (Zoolog.
Jahrbiicher, Section for Anatomy, IV, 1889).
8 This accounts for the occurrence of nuclei with corners or even branches
in the gland-cells of certain insects when in a state of active secretion. I
noticed such nuclei on my series of sections of the ant-inquiline Paussus
cucullatus, which has a strongly marked layer of gland-cells in its antennae.
Similar nuclei occur in the large frontal glands which open through an exuda-
tory pore of the forehead. Cf. ' Zur Kenntnis des echten Gastverhaltnisses
bei den Ameisengasten und Termitengasten ' (Biolog. Zentralblatt, 1903,
pp. 240, 241, 244, 245). ..
4 Cf. R. Hertwig, * Uber Korrelation von Zell- und Kerngrosse fur die
geschlechtliche Differenzierung und die Teilung der Zelle ' (Biolog. Zen-
tralblatt, 1903, Nos. 1 and 2). See also 0. Hertwig, Allgemeine Biologie,
p. 257.
80 MODEEN BIOLOGY
merotomy, and cut unicellular creatures into several parts,1
and the results of these investigations are extremely in-
structive.3
If an Amoeba be cut into several pieces, the part that is
fortunate enough to contain the nucleus continues its previous
way of life ; it moves about and feeds, and so it replaces what
it lost in living substance and recovers its normal size. The
other parts, however, which contain no nucleus, soon cease
to move, and in course of time the network of protoplasm that
forms their body begins to disintegrate, until nothing is left of
them. A non-nucleated fragment of an Amoeba is as incapable
of feeding as it is of moving. It can no longer contract so as to
enclose any particle of nourishment and absorb it into its own
body. If a portion of an Amoeba had already begun such a
nutritive movement before its separation from the main body,
its action is soon arrested and the inactivity of death sets in.
In the case of unicellular Khizopods, which deposit a chalky
shell, this process of secretion, being analogous to the formation
of membrane, becomes impossible as soon as the nucleus is
removed, but the nucleated fragments are able to secrete
a shell wherever a wound has been inflicted.
With regard to plants, too, Klebs has shown 3 that only the
nucleated portions of a plant cell are able to form a new
cellulose membrane, and so to close an opening cut in the
cell-body.
Balbiani has succeeded in establishing,4 by means of
merotomical experiments on Infusoria, the precise part taken
by the chromatin of the nucleus in the nutrition and growth
of unicellular creatures. In a previous chapter (pp. 60, &c.)
we discussed the morphological importance of chromatin or
nuclein in the finer structure of the nucleus ; its physiological
importance is now to be revealed.
In many Infusoria the chromatin is arranged in numerous
1 Merotomy must not be confused with merogony, which is a name given
to attempts to fertilise or develop ova that have been cut up or otherwise
artificially mutilated. We shall refer to this subject again in Chapter VI, § 8.
* Cf. Wilson, The Cell, pp. 342, &c. Also 0. Hertwig, pp. 254, &c.
3 Untersuchungen ausdem botanischen Institutzu Tubingen, 1888, II, p. 552.
4 ' Recherches experimentales sur la merotomie des Infusoires cilies '
(Revue Zoologique Suisse, V, 1889) ; ' Nouvelles recherches experimentales
sur la merotomie des Infusoires cilies ' (Annales d. Micrographie, IV, 1892
and V, 1893).
MEROTOMY OF UNICELLULAE ORGANISMS 81
somewhat coarse granules in the interior of the nucleus.
Balbiani succeeded in cutting a ciliated Infusorian (Stentor)
into three pieces in such a way that the nucleus was also cut,
each segment containing a part of it (fig. 7).
The upper division containing the mouth received four
granules of chromatin, the middle portion received one, and
the lowest three. All three parts of the Stentor continued to
live, and in twenty-four hours each had become a fresh
individual. The one formed from the middle piece of the
FIG. 7.— Stentor.
On the left (a) is the specimen cut into three parts; on the right (b, c, d)
the new specimens formed by regeneration.
k = nucleus ; v = vacuole.
original specimen was, however, considerably smaller than
the other two, because its nucleus had possessed only one
chromatin granule.
In 1896 Lillie succeeded in dividing a Stentor into as many
pieces as he wished, by simply shaking the glass vessel con-
taining it.1 In this way he was able to show that fragments
consisting of only -^ of the creature's volume were capable
of regeneration, provided they contained a particle of the
nucleus ; all non-nucleated portions perished.
In other merotomical experiments made by Balbiani, the
Infusorian was only partially severed, so that the two parts
remained connected by the protoplasm of the cell-body. If the
1 ' On the smallest parts of Stentor capable of regeneration ' (Journal of
Morphology, XII, Part 1).
G
82 MODERN BIOLOGY
nucleus was not cut, the wound healed quickly and the creature
recovered its previous appearance ; it never happened that
two individuals were formed in consequence of a division of
this kind. If, however, the nucleus also was severed, each
part of the Infusorian grew into a new animal, and, as they
were connected by a piece of the protoplasm, the result of this
division was the production of a monstrous double creature
that reminds one of the famous Siamese twins. In course of
time, however, the two individuals began to approach one
another, their nuclei came together and coalesced, and the
monstrosity became one normal specimen.
Other experiments, carried on by Verworn in 1891, l and
Balbiani in 1892 and 1893, have led to a modification of views
based on the experiments just described, inasmuch as they
have thrown additional light on the participation of the
protoplasm in the life of the cell, and so put us on our_guard
against overrating the importance of the nucleus. Verworn
cfiose as the subject of his experiments a spherical Protozoon,
Thalassicola, which measures half a centimetre across, a
gigantic size for a unicellular creature. He succeeded in
isolating the nucleus from the protoplasm of this huge cell-
body, and demonstrated unequivocally that the nucleus cannot
live alone without a particle of protoplasm ; it diecl and did
not lorm a new cell- body On the other hand the non-nucleated
cell-bodies continued alive for a^considerable time and went
on feeding, but tney were unaEle to multiply by means of
division, and so they too eventually died. In his more recent
experiments Balbiani compared very exactly the varying
behaviour of nucleated and non-nucleated portions of Infusoria.
He came to the conclusion that nucleus and cytoplasm are
each the complement of the other in discharging the most
important functions of life, although the nucleus plays the
chief part. Cytoplasm alone was able for some time to pro-
duce the movements of the body and of its ciliated envelope,
the ingestion of food and the contraction of the pulsating
vacuoles of the body. The nucleus was, however, indispensable
to secretion, regeneration, and the processes of division, without
which the cell-plasm must inevitably die.
i ' Die physiologische Bedeutung des Zellkerns ' (Pfluger's Archiv fur die
gesamte Physiologic, LI).
MEKOTOMY OF UNICELLULAE OBGANISMS 83
Not only zoologists, but also botanists, have recently been
making careful experiments with a view to determining the
part taken by the nucleus and the cell-body respectively in
the vital processes of the cell. The results show that in plants
too the value of the cell-body must not be underestimated,
although the nucleus actually controls the vital activity of
the cell.1
I have already (p. 80) quoted Klebs' assertion that frag-
ments of vegetable protoplasm containing no nucleus are
incapable of forming a cellulose membrane. This statement
has been challenged by Palla and others, who think that they
have traced the formation of a new cell-wall in non-nucleated
fragments, although other botanists regard this as very
doubtful.2
Klebs himself mentions the fact that non-nucleated frag-
ments of Algae remained alive for weeks, but eventually died.
I may therefore on this point agree with J. Keinke, the botanist,
when he says : 3 ' The nucleus is unquestionably the most
important organ in the cell-body.'
The total results of these merotomical experiments may be
summed up shortly as follows : — Nucleus and cytoplasm are
both essential to the life of a cell. A cell-body without a
nucleus has no more practical value than a nucleus without
a body of protoplasm. In a normal cell the nucleus is to a
certain extent the central point, the organising principle of the
living matter, or, as Wilson aptly expresses it, ' the controlling
centre of cell-activity.' 4 Nevertheless, after the nucleus has
been removed, the cytoplasm alone is in many cases able for
a time to continue the vital processes already begun, but it
is incapable of producing any notable new formations, and is
absolutely unable to divide and to perpetuate the species.
The nucleus is, as will be shown more clearly in other chapters,
the real bearer of heredity, and within the nucleus in its turn
the chromatin is chiefly concerned with heredity.
The division of an Infusorian into a definite number of
nucleated pieces results in the formation of the same number
1 Further information on this subject will be found in Chapters V and VI,
where I shall deal with cell-division and fertilisation.
2 Cf. Pfeffer, Pflanzenphysiologie, I (1897), pp. 45, &c.
3 Einleitung in die theoretische Biologic, 1901, p. 256.
4 The Cell, p. 30.
o 2
84 MODEKN BIOLOGY
of fresh animals, therefore we are justified in calling the nucleus
the principle of individuation of living matter ; and here again,
within the nucleus, it is to the chromatin that this property
must especially be ascribed, for just as many new individuals
are formed as there are fragments of nucleus containing
chromosomes. If an Infusorian is partially severed, a double
animal is formed only if the nucleus be cut in half.
That the protoplasm of the cell-body is not, however,
without importance in the formation of a living unit seems
to be proved by Balbiani's experiment with the double Stentor.
The nuclei of the two creatures gradually approached one
another, and one normal animal resulted from their coalescence.
If there had been no living bond to unite them, they would not
have grown together again into one animal.
Later on I shall have to discuss the important part played
by the nucleus and its chromatin in the processes of cell-
division and fertilisation. In this place I may, however,
quote a passage bearing on our subject from K. Hertwig's
'Lehrbuch der Zoologie,' 1905, p. 55 (English translation,
p. 67). He is insisting upon the significance of the nucleus,
and says : * The evidence that the nucleus plays the most
prominent role in fertilisation has altered this conception
(of its secondary importance). Then arose the view that
the nucleus determines the character of the cell ; that
the potentiality of- the protoplasm is influenced by the
nucleus. If from the egg a definite kind of animal develop,
if a cell in the animal's body assume a definite histological
character, we are, at the present time, inclined to ascribe
this to the nucleus. From this, then, it follows further that
the nucleus is also the bearer of heredity ; for the transmission
of the parental characteristics to the children (a fact shown
to us by our daily experience) can only be accomplished
through the sexual cells of the parents, the egg- and sperm-
cells. Again, since the character of the sexual cells is deter-
mined by the nucleus, the transmission in its ultimate analysis
is carried on by the nucleus.' l
1 For the biological and physiological importance of the nucleus, see also
Wilson, The Cell, pp. 358, 359.
CHAPTER V
THE LAWS OF CELL-DIVISION
1. VARIOUS KINDS OF DIVISION OF THE CELL AND NUCLEUS.
Various kinds of division of the cell (p. 86). Various kinds of division
of the nucleus (p. 87). Direct division of the nucleus (p. 87).
Indirect division of the nucleus (karyokinesis or mitosis) (p. 88).
2. VARIOUS STAGES OF INDIRECT DIVISION OF THE NUCLEUS.
Prophase (spireme or monaster stage) (p. 90). Metaphase (the chromo-
somes split lengthwise) (p. 94). Anaphase (rearrangement of the
chromosomes) (p. 94). Telophase (dispireme or diaster stage)
(p. 95).
3. GENERAL SURVEY OF THE PROCESS OF KARYOKINESIS.
The part played by the centrosomes (p. 98). Debated points regarding
their importance, occurrence, and origin (p. 99). Conclusions
(p. 101).
In a previous section (p. 66) we spoke of the cells as the
bricks composing the building of the organic world. But
they are at- the same time the architects, always rebuilding
the organic world in an unbroken series of generations. They
are living constituents, growing and multiplying in virtue of
the laws of development imposed upon them, and they unite
to form tissues, organs, and living creatures of various kinds.
The fundamental process upon which the architecture of the
cell depends in all multicellular organisms is that of cell-
division. What the delicate scalpel of the scientist effects
violently, when he vivisects unicellular organisms (see p. 80),
is done automatically under certain circumstances, in accord-
ance with the interior laws of organic growth ; and one cell,
by dividing, forms two or more.
Let us now study this natural cell-division and the interest-
ing processes that attend it.
1. VARIOUS KINDS OP DIVISION OF THE CELL AND NUCLEUS
Whenever the development of an individual requires an
increase in the number of cells, whether to make new tissues,
or to enlarge those already existing, or to form new creatures
85
86 MODEKN BIOLOGY
and carry on the process of propagating the species, — in every
case the cells concerned have to divide. In cells containing one
nucleus, the first step is the division of the nucleus. Then
the protoplasm of the cell-body either divides too, or remains
undivided ; l in the latter case a uninuclear cell becomes multi-
nuclear ; in the former, which is much more common, one cell
becomes several. If the cellular membrane is divided and
fresh cell-walls are formed, we have exogenous cell-division ;
but if the daughter-cells remain within the membranous
covering of the mother-cell, we have what is called endogenous
cell-division.2 When exogenous cell-division takes place,
the new cells either remain side by side, so that a cellular
tissue is formed, or they leave their homes and migrate.
Again, when a cell divides, it may form two or more cells of
equal size, and this is simple cell-division ; or the new cells
cut off from the mother-cell may be much smaller than it is ;
this kind of division is called gemmation — it occurs in the growth
and multiplication of many of the lower animals, for instance,
in the Podophrya, the Hydra, &c., and in some plants, such as
the yeast fungus. Whatever be the form of cell-division, its
chief feature is invariably the division of the nucleus, and we
must therefore devote attention particularly to it. We
here touch upon a subject with regard to which modern micro-
scopical research has been most successful ; in fact, it would
be difficult to name any other subject in dealing with which
microscopical research has produced more brilliant results,
so great have been the delicacy and intelligence with which
the investigations have been conducted, and so bold and
shrewd the conclusions deduced from their results, although
these conclusions are to a large extent still hypothetical.
Modern cytology has succeeded in some degree in solving the
mysteries of heredity, by means of microscopical research.
If we are careful to distinguish the actual results from
the conclusions deduced from them, we shall be able
1 The process of division which affects only the nucleus and does not result
in a cell-division is sometimes called ' free nuclear division.' (Cf. Strasburger,
Lehrbuch der Botanik, 1895, pp. 55, &c. Eng. trans. 1893, pp. 89, 90.) This
free nuclear division must not be confused with ' free formation of the nucleus,'
to which I shall refer later.
2 On the subject of endogenous increase of nuclei, resulting in the presence
of several nuclei in one cell, see 0, Hertwig, Allgemeine Biologie, 1906,
pp. 213, &q,
NUCLEAK DIVISION 87
subsequently to form a true opinion of the modern theories of
heredity.
Nuclear division is either direct or indirect. In the former,
the division of the nucleus takes place without causing any
essential change in its structure ; but in the latter it is accom-
panied by a complicated mechanism, involving great changes
in the structure of the nucleus, and partially also in the proto-
plasm of the cell. These changes are chiefly in the position
and arrangement of the chromatin constituents of the nucleus,
viz. the nuclear thread and its chromosomes ; but there are
also no less regular formations of fibres and asters out of the
achromatic nuclear substance.
On account of the characteristic movements of the chromatin
in the nucleus, the indirect nuclear division is sometimes called
karyokinesis (nuclear movement), while the transformation
FIG. 8. — Direct division of the nucleus in red blood-corpuscles.
and breaking up of the chromatin thread and the simultaneous
appearance of achromatic spindle fibrils have given rise to the
name mitosis (/uro? = thread) or mitotic division, whereas the
direct division is called amitotic. Let us begin by considering
the latter, as it is the simpler form, and will help us to under-
stand the more complex process of indirect division.
Direct division of the nucleus was observed by Remak in
red blood-corpuscles as early as 1841. Young corpuscles
contain one nucleus, the division of which leads to their multi-
plication. The process is very simple, as the accompanying
figure will show.
The nucleus in the cell is at first spherical, then it elongates,
gradually contracting in the middle. At the same time the
cell itself assumes an oval shape, having previously been
round. The nucleus next splits in half, and the two halves
retire from one another ; then the protoplasm of the cell-body
contracts in the middle, the indentation deepening until finally
two spherical blood-cells are formed, each with a round nucleus
88 MODEKN BIOLOGY
in its centre. Therefore, in the course of direct cell-division,
the nucleus by simply contracting breaks into two, and then
the protoplasm of the cell-body and the cellular membrane
divide likewise. This form of division of the nucleus and cell
occurs frequently among Protozoa, especially among those
possessing a nucleus that is rich in chromatin.
There is some uncertainty as to the discoverer of indirect
division. Wilson (' The Cell,' p. 64) ascribes the discovery of
mitosis to Anton Schneider, a zoologist, in 1873. Sachs thinks
J. Tschistiakoff,1 a botanist, has a better claim to the honour,
as his work, published in 1874, gave the first impulse to modern
research on this subject. Others again mention E. Strasburger,
the botanist, as the discoverer of this complicated form of
cell-division. There is no doubt that the German anatomist,
Walter Flemming, was the first to formulate and expound the
process of mitosis in his ' Beitrage zur Kenntnis der Zelle
und ihre Lebenserscheinungen ' (1 878-82). 3 Abbe Carnoy, a
Belgian, has thrown much light upon the subject in his
' Biologie cellulaire ' (1884), and by means of his admirable
study of cell-division in Arthropods.3
It would be superfluous to mention more names, for the
study of mitosis has now become a favourite branch of cyto-
logical research, and we know that, in the case of very different
kinds of tissue, indirect division of the nucleus occurs far more
generally than direct. The two great forms of division of
nucleus and cell are, however, connected by various inter-
mediate forms.
A very thorough discussion of all the phenomena observed
in mitosis may be found in Wilson's ' The Cell/ pp. 65-121, a
book that I have frequently had occasion to mention. My
own account of the process must be limited to the barest outlines.
2. VARIOUS STAGES OF INDIRECT DIVISION OF THE NUCLEUS
We have seen that in direct division of the nucleus, or
amitosis, the division of the chromatin elements of the nucleus
1 Sachs, Vorlesungen fiber Pflanzenphysiologie, 1887, p. 115, note 4. Tschi-
stiakoff's work to which Sachs refers is his ' Materiaux pour servir a 1'histoire
de la cellule vegetale ' (Nuovo Giornale Botan. Ital. VI). See particularly
Plate VII, figs. 11-13.
2 Archiv Jur mikroskopische Anatomie, XVI-XIX.
8 ' La Cytodierese chez les Arthropodes ' (La Cellule, I, 1885, No. 2).
NUCLEAR DIVISION 89
in the mother-cell, so as to form the nuclei of the two daughter-
cells, is effected by means of a rough partition of the mother-
nucleus, which first contracts in the centre and then splits
in half. In indirect cell-division, or mitosis, there is a
complicated series of phenomena, all aiming at dividing the
chromatin of the mother-nucleus in a most exact and regular
fashion between the two daughter-nuclei. This may be called
the fundamental idea underlying the whole process of karyo-
kinesis or mitosis, and all the other incidents are subordinate
to it.
It is, however, as E. B. Wilson rightly remarks, difficult to
give a connected general account of mitosis, because the details
vary in many respects in different cases, and especially because
great uncertainty still hangs over the nature and functions of
the so-called centrosome. In German textbooks of zoology
we generally find the process of karyokinesis exemplified by
the nuclear divisions of the epithelial cells of the spotted
salamander (Salamandra maculosa), and my own experience
shows that these supply us with an excellent means of tracing
the process of karyokinesis conveniently. It is only necessary
to cut off a piece of the epidermis from the tail of a salamander
or triton larva, to treat it in the usual way with carmine or
haematoxylin, so as to prepare it for the microscope, and then
it is possible to see a series of karyokinetic figures in the cells
of the epithelium. In order to be able to distinguish the
single chromosomes, we generally have recourse to some
special staining methods, and Heidenhain's stain with iron-
haematoxylin can still be recommended. In discussing the
subject, however, I shall refrain from alluding to differences in
single instances and in staining methods, and shall follow
Wilson's admirable account of karyokinesis in ' The Cell,'
pp. 65-72.
We may distinguish four groups of phenomena as four
successive stages in karyokinesis. There are : — (1) the
Prophase or preparatory changes ; (2) the Mesophase or
Metaphase, in which the chromatin substance of the nucleus is
actually divided ; (3) the Anaphase, in which the divided
nuclear elements are rearranged so as to form the daughter-
nuclei ; (4) the Telophase, in which the cell finally divides
and the daughter-nuclei return to the state of rest.
90 MODEKN BIOLOGY
These four stages are, of course, not sharply marked off
from one another, but one gradually passes into another.
In all four we see a double series of changes going on
simultaneously in the cell. The first involves the chromatin
figures of the nucleus, formed by the change in position and
the halving of the chromatin substance of the nucleus ; the
second series involves the achromatic nuclear figures, resulting
from changes in the achromatic nuclear framework, and to
some extent also from changes in the achromatic cell-frame-
work. The first series of changes effects the actual division
of the nucleus ; the second series is subsidiary, and consists of
a radiating arrangement of the protoplasm, rendering possible
the movements that occur in the first series.
Let us now examine some diagrams (figs. 9-16) which
will give us a better idea of the marvellous mechanism of
karyokinesis.
1. Prophase. — The first step towards indirect division of the
nucleus is a change in the chromatin substance. When the
cell was resting, this appeared as a coil of thread or as a reticular
or alveolar framework, but now it thickens into a skein. Fig. 9
represents a cell at rest, with its reticular chromatin frame-
work of the nucleus. The dark spot n within the network is
a nucleolus (see pp. 54 and 61), but its presence is not
essential ; c is the centrosome already in process of division —
it is a spherical body, only slightly susceptible to stains, which
is also called the polar body, from its position. Boveri terms
it the organ of cell-division, and he is probably right in so
doing, as we shall see later.1
In Fig. 10 the prophase of karyokinesis has begun, and
the chromatin thread of the nucleus has thickened and con-
tracted, so as to form one unbroken skein. The nucleolus n is
still visible, the centrosome has divided, so that there are now
two, which are moving apart and beginning to send out delicate
rays of protoplasm to form the attraction-sphere a. This is
sometimes called the chromatin skein or spireme stage of cell-
division, from the arrangement of the chromatin substance of
the nucleus. As it often forms a kind of rosette, it has also
been described as the chromatin monaster (single star) stage.
1 This polar body must not be confused with the directing or polar globule
of the egg-cell. See Chapter VI, § 2.
NUCLEAK DIVISION
91
Lastly, as the achromatic centrosome figure (a in fig. 10)
resembles a double star, it is sometimes called the achromatic
amphiaster stage. The farther apart the two centrosomes
move in order to take up their position at the opposite poles
FIG. 9.
FIG. 10.
FIG. 11.
FIG. 12.
FIG. 9. — Cell with resting nucleus.
FIGS. 10-12. — Prophases of mitosis (Wilson).
c — centrosome ; n = nucleolus ; a — amphiaster ; sp = spindle ;
chr = chromosomes ; aek = equatorial plate.
of the nucleus, the more applicable becomes the name amphi-
aster to this achromatic figure.
Fig. 11 represents the second stage of prophase. The
double star or amphiaster now forms an achromatic spindle,
and the chromatin figure shows remarkable changes. The
92 MODEKN BIOLOGY
chromatin spireme thread has broken up into a number of
regular segments, which form the chromosomes. They
originally composed the chromatin network of the nucleus,
and at each cell-division they appear in the same shape and
number.1
Tlje chromosomes of the same nucleus are generally all of
the same size and shape, but occasionally they form a series
of pairs, and in some very rare cases superfluous or accessory
chromosomes appear. They have, as a rule, the shape of a
fairly regular U or V, sometimes however they are rod -like or
even spherical. In certain cases the lengthwise division of the
chromosomes, which takes place in the metaphase, is suggested
previously, as each splits lengthwise into two parallel parts,
which remain connected by delicate transverse fibres. (See
the chromosomes in fig. 11.)
As we shall see in the next chapter, the chromosomes
are of very great importance in the propagation of the race
and in the transmission of hereditary characteristics, and
therefore we must devote a little more attention to them.
In all plants and animals propagated by the union of two sexes,
the number of chromosomes in every cell is invariably even,
one half being derived from each of the parents. Further,
with very few exceptions, every species of plant and animal
has always the same fixed number of chromosomes in every
cell.3
Only the germ-cells are an important class of exceptions,
as we shall see in the next chapter, for they contain only half
as many chromosomes as the other cells of the body.
The number of chromosomes in each cell varies very greatly
in different species of animals and plants. It ranges from 2
to 168. Sometimes there is a considerable difference in the
number of chromosomes of closely related species, whilst
on the other hand those of unconnected species are often
identical in number. Any one who is interested in the subject
may find the chromosome numbers of sixty-two species of
1 Boveri has based his theory of the individuality of chromosomes upon
this fact. See Chapter VI, § 9.
2 The threadworm, Ascaris megaJocephala, has two varieties, one of which
contains four, and the other two, chromosomes in the cells of its body. For
other instances see Korschelt and Heider, ' Lehrbuch der vergleichenden
Entwicklungsgeschichte der wirbellosen Tiere ' (Allgem. Teil, part 2, p. 612).
NUCLEAK DIVISION 93
plants and animals tabulated on p. 206 of Wilson's ' The
Cell.' i
I quote from it a few numbers by way of example ; they
are those of the chromosomes in the somatic cells of each
species ; in the ripe germ-cells, as has been said before, only
half the number of chromosomes occurs.
In many worms there are 2 or 4 chromosomes ; in
others 8 ; in some Medusae, grasshoppers and Phanerogams,
12 ; in one Hydrophilus, a snail, the ox and man, 16 ; in
the sea-urchin and a sea -worm (Sagitta), 18 ; in an ant (Lasius),
20 ; in the lily, the salmon, the frog and the mouse, 24 ; in the
torpedo, 36 ; in a worm (Ascaris lumbricoides), 48 ; and in a
little fresh -water crab (Artemia), 168.
Let us now turn to fig. 11, and follow the movements of the
chromosomes during karyokinesis. We see that the chromatin
within the nucleus now appears as an independent formation.
The nuclear membrane enclosing the nucleus has meantime
disappeared, and so has the nucleolus (n in figs. 9 and 10). 2
The two centrosomes, which in fig. 10 are still above the
nucleus, have now taken up their position at its two poles.
The protoplasmic rays proceeding from them have grown
longer, and now meet in the centre of the nucleus forming the
nuclear spindle (sp). This is also called the direction spindle,
because it serves to direct the chromosomes in their movement
both before and after the actual division. The chromosomes
now lie apparently free in the middle of the cell, but in reality
they are connected with the fibres of the achromatic spindle,
which are, as a rule, formed out of what was previously the
achromatic nuclear framework, but in some cases out of the
cell framework, or out of both together.3
This stage (fig. 11) is called, from the chromatin nuclear
figure, the stage of chromatin loops, or, from the achromatic
figure, the stage of the direction spindle.
1 Of. also 0. Hertwig's Allgemeine Biologie, 1906, p. 203, where the same
table is given with some additions.
2 On the behaviour of nucleoli in different cases, see Wilson, The Cell,
pp. 67, 68.
3 There was for a long time great divergency of opinion regarding the
origin of the protoplasmic spindle-fibres. Modern research seems to show
that we ought to distinguish three kinds of spindle : (a) those that are formed
of the nucleus alone ; (6) those that are formed of the cell cytoplasm ; and
(c) those that are of mixed origin. Cf. 0. Hertwig, Allgemeine Biologie, 1906,
pp. 193-195.
94 MODEEN BIOLOGY
Fig. 12 depicts the third part of the prophase, which
leads on to the metaphase. The chromosomes are moving
along the spindle-fibres towards the centre, and finally group
themselves in the form of a ring in a plane passing through
the equator of the spindle, which is known as the equatorial
plate.1
From the chromatin nuclear figure, this stage is called that
of the equatorial plate, or rather crown (aek in fig. 12), because
the chromosomes remain distinct from one another, and only
group themselves in the shape of a ring. The achromatic
nuclear figure, the spindle (sp), is best seen in this stage.
2. Metaphase. — The middle stage, or metaphase, now
begins, and is the culminating point of the whole karyokinesis,
because in it the actual division of the nucleus takes place
(fig. 13). In 1880 W. Flemming discovered that this division
consists of the splitting of the chromosomes lengthwise into two
exactly similar halves. If each chromosome had originally the
shape of a V, it now becomes a W ; if it was a simple rod, it is
now a double one. This division of the chromatin nuclear
substance takes place with such extraordinary exactitude,
that it is impossible to avoid regarding it as of great importance
to the processes affecting heredity. As W. Eoux showed in
1883, the entire chromatin of the nucleus in the mother-cell is
divided according to the strictest rules of distributive justice,
so that the nuclei of the daughter-cells receive precisely equiva-
lent portions, and each portion is arranged in exactly the same
number of chromosomes as there were in the mother-cell.
It is a matter of indifference whether the lengthwise splitting
of the chromosomes in the metaphase was anticipated by a
longitudinal division of each single chromosome (fig. 11), or
whether the whole process takes place at once. The nucleolus n
may remain visible during the metaphase (as in fig. 13) or it
may disappear. Its behaviour is of minor importance.
This central stage of indirect cell- division, which we have
just described, is known as the stage of doubling the equatorial
crown.
3. Anaphase. — In this stage the daughter-nuclei of the
1 For the sake of simplicity, the chromosomes on the diagram are repre-
sented as rod-like rather than curved, although the latter is the more usual
form. Each loop points to the centre of the equatorial plate.
NUCLEAK DIVISION
95
new cells are built up. After splitting lengthwise in the
metaphase (fig. 13), the two halves of each chromosome
begin to draw apart. Those on the right group themselves
about the right pole of the spindle, and those on the left about
the left pole, the spindle-fibres serving as guides. Fig. 14
FIG. 13. — Stage of metaphase.
FIG. 14. — Stage of anaphase.
FIGS. 15 AND 16. — Stages of telophase (Wilson).
c = centrosome ;
ep = equatorial plate ;
n = nucleolus ;
pk = polar caps ;
if = interzonal fibres ;
zp = cell-plate.
represents this stage of the anaphase. It is known as that of
dicentric orientation of the daughter-chromosomes.
4. Telophase. — The process of karyokinesis now advances
rapidly through its final stages or telophase. Fig. 15 represents
the transition from the anaphase to the telophase. The
chromosomes of the daughter-nuclei have now reached the
two opposite poles of the spindle, have grouped themselves
together and sent out delicate fibres, which bind them together
96 MODERN BIOLOGY
and will eventually enable them to unite and form the
chroma tin framework of the daughter-nuclei. In some
cases the chromosomes do not directly coalesce to form the
new nuclear framework, but it is produced by the fusion of
vesicles to which the chromosomes have given rise (vacuoli-
sation).1 From the chromatin nuclear figure, which forms a
dark coloured ring round the two poles of the cell in course of
division (fig. 15), this stage has been called that of the two
polar caps or crowns. If these crowns assume a stellate
shape, it is called the stage of the chromatin diaster or double
star. When, as in the epithelial cells of Amphibia, the egg-
cells of Ascaris and many plant cells, the chromatin framework
of the new daughter-cells is not produced by vacuolisation of
the chromosomes, but by their thickening and growing together,
the chromatin diaster stage is followed immediately by that
of the chromalin dispireme. We can form some idea of this, if
we imagine the ends of the chromosomes within the future
daughter-cells in fig. 15 to be united. This would produce
two skeins similar to that which we noticed in the prophase
(fig. 10) as the beginning of the division of the chromosomes.
The fibres of the spindle, which appear in fig. 15 uniting
the two chromatin asters, have now another name. They
are called interzonal or connecting fibres (if). In almost all
plant cells, and occasionally in animal cells, they are thickened
in the middle, and these thickened portions subsequently
make up the cell-plate (zp) or mid-body of the dividing cells.
At the end of the telophase we reach the last stage of
indirect division of the nucleus (fig. 16). The two chromatin
skeins of the daughter-nuclei have surrounded themselves
with a membrane, within which the new framework has been
formed. We can again perceive the nucleolus (n) in the
nucleus. Each daughter-nucleus has brought with it a
centrosome into the new cell, where it will divide, and the
two fresh centrosomes will move from the poles to the two
sides of the equator of the original karyokinetic figure and
take up their position there. This is, however, not always
the case. Sometimes they vanish altogether, and reappear
only when the process of division is to begin again. The fate
1 For further information regarding the growth of the nucleus, see Wilson,
The Cell, p. 71.
PHENOMENA OF KABYOKINESIS 97
of the interzonal fibres (if), which remind us of the spindle
of the former achromatic karyokinetic figure, varies greatly.
In plant cells they remain, and by thickening they help to
build up the new cell-walls formed by the secretion of cellulose.1
Fig. 16 gives us an instance of this. The perpendicular line
in the middle represents the cell-plate (zp) or mid-body of
the cell in course of division. In animal cells, on the contrary,
the interzonal fibres generally disappear early and no trace
of them remains, as they are not in this case needed to form
a cell-plate. Fig. 15 shows the mother-cell with deep indenta-
tions above and below ; these increase until it finally splits
in half, and the two daughter-cells are formed, and thus
the process of indirect division of the nucleus and cell is
completed.
3. GENERAL SURVEY OF THE PROCESS OF KARYOKINESIS
Let us review once more the phenomena of karyokinesis.
The first two stages of the prophase, those, namely, of the
chromatin spireme and the chromatin monaster, correspond
exactly to the last two stages of the telophase, those of the
chromatin diaster and the chromatin dispireme. The stages
lying between these two extremes belong to the doubling of the
equatorial plate or crown. This culminating point is connected
on the one hand with the prophase, by the breaking up of the
chromatin monaster into V-shaped segments, and by their group-
ing to form a simple equatorial plate ; it is connected on the
other hand with the anaphase, by the dicentric orientation of the
daughter-segments in the double equatorial plate, and with the
telophase by their withdrawal to the poles and formation of
the two polar caps or crowns. Indirect karyokinesis is there-
fore a process that is at once marvellously complex in its
conformity to law, and wonderfully simple in design. Its
object is to divide the chromatin of the nucleus in the mother-
cell into two absolutely equal parts, in such a way that the
nucleus of each of the two daughter-cells shall receive the half
of every chromosome in the mother-cell, and that the number
of chromosomes in each daughter-nucleus shall be the same
as that of the chromosomes in the mother-nucleus.
1 Cf Strasburger, Lehrbuch der Botanik, 1895, p. 52.
98 MODEKN BIOLOGY
The account just given of indirect karyokinesis and the
diagrams illustrating it must be regarded as in some degree
theoretical, for many modifications occur in various kinds of
animals and plants.1
Reinke says very truly in his i Einleitung in die theoretische
Biologie,' p. 260 : ' To variations in the structure of the nucleus
in different organisms correspond variations in the course of
mitosis, as will be seen by comparing them. But we find every-
where four fundamental phenomena, viz. the formation of the
chromatin and achromatic figures out of the resting nucleus ;
the splitting of the chromosomes ; the movement of the
divided chromosomes to the poles of the mitotic figure ; and
the rearrangement of the parts so as to reproduce the configura-
tion of the resting nucleus. The persistence of the number
of chromosomes from generation to generation in nuclei of
the same species may be added as a fifth point.'
The polar bodies called centrosomes were discovered by
Flemming in 1875,2 and I have designated them and the
spindle radiating from them a biomechanical contrivance for
securing a regular division of the chromatin. This view is
confirmed by the account of karyokinesis given by the best
authors. We may therefore follow Boveri, Weismann, and
others in calling the centrosomes the especial organs of cell-
division.3
E. Bergh is inclined to ascribe even greater importance in
the process of cell-division to the achromatic than to the
chromatin nuclear figure.4 E. "van Beneden, Flemming,
Guignard and others are. also, perhaps, disposed to overrate
the importance of the centrosomes.5
1 This is true of the normal processes concerned in karyokinesis, but
there are other modifications which are matters of pathology, and which
we cannot discuss here. See 0. Hertwig, Allgemeine Biologie, pp. 214, &c.
2 On the subject of centrosomes see 0. Hertwig, Allgemeine Biologie,
pp. 45-49, 195, &c., and E. B. Wilson, The Cell, pp. 50, &c., 74, &c., 101, &c.,
208, &c., 354, &c. '
3 In the next chapter we shall have to examine Boveri's opinion regarding
the importance of the centrosomes as fertilising elements. Cf. also Boveri,
Zellenstudien, Part 4. 'Uber die Natur der Centrosomen' (Jenaische Zeit-
schrift fur Naturwissenschaft, 1901).
4 'Kritik einer modernen Hypothese von der Ubertragungerblicher Eigen-
schaften ' (Zoologischer Anzeiger, XV, 1892, No. 383).
5 See also V. Haecker, ' Uber den heutigen Stand der Centrosomenfrage '
(Verhandl. der Deutschen Zoologischen Gesellschaft, 1894, pp. 11-32). This work
is a standard one, but only for the state of knowledge on the subject when it
was written.
PHENOMENA OF KABYOKINESIS 99
Fol's famous * Quadrille oi Centres/ which the two halves of
the male and female centrosomes were supposed to dance round
the segmentation nucleus of the fertilised egg-cell, has proved
to be erroneous^ Strasburger and his followers l "think that
centrosomes are wanting in the higher kinds of plants,
and in the division of Protozoa they are either altogether
absent or of rare occurrence. They are present in the
segmentations of the nucleus which lead to the formation
of spindle-poles before fertilisation in the sun-animalculae
(Actinosphaerium) .3
If centrosomes were absolutely essential to the action of
heredity, they would inevitably be present whenever cells
divide, or at least whenever those cells divide which are con-
nected with the preservation of the species, and this is not
the case.
The whole question of the function of centrosomes is still
involved in much obscurity, and Strasburger sums up the^
difficulties admirably in the following words : 3 ' At the present
moment and at the present state of our investigations, I must
content myself with the thought that individualised centro-
somes disappear in the more highly organised plants. Why
otherwise should we fail to trace them in any of the Pterido-
phyta and Phanerogams, whilst we succeed in the Bryophyta,
(Mosses) ? I am quite willing to agree with Flemming, who
thinks it possible that in the future centrosomes will be found
also in the higher plants. ... No one as yet has been able to
form a conclusive opinion regarding the origin, structure,
function, persistence or disappearance of the centrosomes
whilst the cell is at rest, nor is much known as to their dis-
tribution, although the reasons brought forward by Flemming
for believing them to occur everywhere seem very weighty,
when considered separately. Carnoy, however, takes a decidedly
opposite view.'v
We must refer our readers to Wilson and 0. Hertwig for
further information on the subject of centrosomes. These
two writers have collected a quantity of material involving
1 Histologische Studien aus dem Banner Botanischen Institut, Berlin, 1897.
2 0. Hertwig, Allgemeine Biologie, 1906, p. 189. *
3 ' tiber Reduktionsteilung, Spindelbildung, Centrosomen und Cilien-
bildner im Pflanzenreich ' (Histolog. Beitrdge, 1900, Part 6, pp. 170, 171).
H 2
100 MODEEN BIOLOGY
much research. Strasburger concludes with a reference to a
theory based on recent research, according to which the cen-
trosome is a mass of kinoplasm, not only serving the purpose
of cell-division, but also concerned in the movement of the
flagella and cilia of many cells and especially of the spermatozoa.
0. Hertwig has adopted this view in his ' Allgemeine Biologie,'
1906, p. 122, &C.1
As Strasburger says in the above quotation, we still know
very little as to the origin of the centrosomes. Some regard
them as composed of the protoplasm of the cell ; others, with
more probability, think that they are a product of the nucleus.
A new theory is that the centrosomes are not permanent con-
stituents of the cell,2 but are merely microsomes, representing
a part of the achromatic framework of the cell or nucleus,
which have a temporary importance during the processes
involved in karyokinesis, inasmuch as such a microsome, by
taking up its position at the pole of the nucleus in course of
division, becomes the focus of the protoplasmic rays from
which the spindle proceeds. If this theory is true, the cen-
trosomes, and the attraction sphere which they form, are
perhaps not the causes of nuclear division, but a result of the
beginning of the process. Mitrophanow tried to prove this
theory as early as 1894, in his * Contribution a la division
cellulaire indirecte chez les Selaciens ' (Journal international
d'anatomie et de physiologic, XI).
Wasilieff thinks that the centrosome is only a temporary
product of the joint action of nucleus and protoplasm ; 3 and
this theory is supported by experiments (to which reference
will be made in the next chapter) by Morgan, Loeb and
Wilson, who succeeded in artificially producing centrosomes
in the unfertilised eggs of sea-urchins by means of salt
solutions.
The astral rays of the nuclear spindle may all be formed of
1 See also Ikeno, ' Bleptutoplasten im Pflanzenreich ' (Biolog. Zentralblatt,
XXIV, 1904, No. 6, pp. 211-221). Recent investigations made by Russo and
di Mauro in 1905, and by Gemelli in 1906, seem however to show that the
flagella and cilia are not connected with the centrosomes, but with special
basal bodies formed by a thickening of the cell- wall.
2 Cf . the views expressed by Brandes and Flemming in the Verhandlungen der
Deutschen Zoolog. Gesellsckafi, 1897, pp. 157-162.
3 ' tiber kiinsthche Parthenogenesis des Seeigeleis ' (Biolog. Zentralblatt,
XXII, 1902, No. 24, pp. 758, &c.).
PHENOMENA OF KAKYOKINESIS 101
the achromatic nuclear framework, or of the spongioplasm
of the cell-body, or they may have a mixed origin.1
We really know nothing of the cause producing this radia-
tion, nor do we know what makes the V-shaped loops of
chromatin split in half lengthwise.3
The only certain facts are that karyokinesis depends upon
the partition of the chromosomes, and that the protoplasmic
rays of the nuclear spindle determine the direction in which
the chromosomes move. We are also convinced that great
importance in the processes of evolution must be assigned to
the persistence in the number of chromosomes contained in
the somatic cells of individuals belonging to one and the same
species, which number is most accurately preserved during
karyokinesis by the longitudinal division of the chromatin
loops. If we compare this normal form of mitosis with the
method of dividing the chromatin in the germ-cells (cf . the next
chapter) we shall lay still greater stress upon the importance
of this point. We must, however, remember that the science
of the present day is quite unable to tell us anything about
the inner causes that produce the wonderfully complicated
phenomena observed in indirect karyokinesis.
' We must acknowledge that we are not in a position to
form any plausible theory at all as to the kind of reciprocal
1 Cf . Henking, ' tlber plasmatische Strahlungen ' ( Verhandl. der Deutschen
Zoolog. Gesellschaft, 1891, pp. 29-36) ; also Yves Delage, La structure du
protoplasma, 1895, p. 75 ; O. Hertwig, Allgemeine Biologie, pp. 192, etc.
2 Cf. also H. E. Ziegler, ' Untersuchungen iiber die Zellteilung ' ( Verhandl.
der Deutschen Zoolog. 'Gesellschaft, 1895, pp. 62-83.) A great number of
theories have been advanced to account for the nuclear figures in karyokinesis,
but none of them can claim a high degree of probability. This remark applies
to Ziegler's own comparison of these figures with the lines of force in a magnetic
field. Yves Delage (pp. 310-314) gives a good summary and criticism of the
various theories regarding the causes of cell-division and of the formation of
karyokinetic figures. He says with much truth of the comparatively best
of these theories — that, viz., advanced by Henking — that it would be just
as reasonable to see in the lion, the scales, and the fish of the zodiac a real
lion, real scales and real fish, as to act like the propounders of these theories,
and pretend that their mechanical representations of cell-structures and
karyokinetic figures are real cell-structures and real figures. Another attempt,
no more satisfactory than its predecessors, at explaining the mechanism of
cell-division has been made quite recently by V. Schlapfer in his article 'Eine
physikalische Erklarung der achromatischen Spindelfigur und der Wanderung
der Chromatinschleifen bei der indirekten Zellteilung ' (Archiv fur Entwick-
lungsmechanik, XIX, 1905, pp. 107-128). It is an undoubted fact that many
physical and chemical influences are at work in the process of karyokinesis,
but we possess as yet very little real knowledge of their power to direct and
further the biological aim of the division of cell and nucleus.
102 MODEBN BIOLOGY
action existing between the cell-body and the nucleus. We
have no foundations of facts upon which to construct a theory.' l
Whoever cares to see a summary and criticism of the various
hypotheses regarding the mechanism of mitosis propounded by
E. van Beneden, Heidenhain, B. Hertwig, Fol, &c., may refer
to Wilson, ' The Cell,' pp. 100-111. His resume of the whole
discussion is as follows : ' A review of the foregoing facts
and theories shows how far we still are from any real under-
standing of the process involved either in the origin or in the
mode of action of the mitotic figure ' (p. 111).3
The secret physiological causes that motive cell-division are
unknown to the scientist, whose microscope reveals to him
only their morphological action. They are a problem of
cellular physiology, a problem containing in itself the whole
mystery of life. We have now to trace this mystery in the
phenomena of fertilisation and heredity, and we shall be able
to approach its solution in Chapter VIII, where we shall deal
with the processes of organic development.
1 Korschelt and Heider, Lehrbuch der vergleichenden Entwicklungs-
geschichte (Allgem. Teil, Part I, pp. 153, 154).
2 See also Wilson's chapter on ' Some problems of cell-organisation.'
CHAPTER VI
CELL-DIVISION IN ITS RELATION TO FERTILISATION
AND HEREDITY
(See Plates I and II)
INTRODUCTORY REMARKS. AIDS TO THIS INVESTIGATION.
1. THE PROBLEMS TO BE SOLVED.
2. THE MATURATION-DIVISIONS OF THE GERM-CELLS.
Their general features. Reduction in the number of chromosomes (p. 110).
Varieties of maturation -divisions. Equal division and reducing
division. The eumitotic type (p. 111). The pseudomitotic type and
its subdivisions (p. 111). Difficulties in interpreting microscopical
observations. Diagrams representing the maturation-divisions of the
egg-cell (p. 118).
3. THE NORMAL PROCESS OF FERTILISING AN ANIMAL O\UM.
Echinus type and Ascaris type of nuclear union (p. 120). More detailed
description of the process of fertilisation (Boveri) (p. 123). Equal
distribution of the chromatin nuclear constituents of both parents
to the segmentation-cells. Apparent exceptions (p. 125). Boveri's
view of the importance of the male centrosome in fertilisation
(p. 126).
4. THE PHENOMENA OF SUPERFECUNDATION AMONG ANIMALS AND DOUBLE-
FERTILISATION IN PLANTS.
Pathological and physiological polyspermy. Double-fertilisation in the
Angiosperms (p. 128). Specific polyembryony (p. 129).
5. THE PROCESSES OF CONJUGATION IN UNICELLULAR ORGANISMS AND THEIR
RELATION TO THE PROBLEM OF FERTILISATION.
Conjugation of ciliate Infusoria. Transition from the conjugation of
lower organisms to the fertilisation of higher organisms (p. 131).
Comparative deductions (p. 134).
6. NATURAL PARTHENOGENESIS.
Variations in the behaviour of the polar bodies and in the chromatin
reduction (p. 136). Parthenogenesis in the vegetable kingdom.
Conclusipns (p. 138).
7. ARTIFICIAL PARTHENOGENESIS.
Account of various experiments and their results (p. 139). Behaviour of
the astrospheres (p. 142). Bearing of these experiments upon the
problem of fertilisation (p. 144). Morphological and chemico-
physical theories of fertilisation (p. 145).
8. FERTILISATION OF NON-NUCLEATED EGG-FRAGMENTS (MEROGONY).
Account of various experiments and their results (p. 149). Boveri's
'organisms without maternal qualities' (p. 152). Ziegler's experi-
ments on the constriction of sea-urchins' eggs (p. 153). Importance
of the spermato-centrosome in division of the egg-cell (p. 154).
103
104 MODEEN BIOLOGY
9. REVIEW OF THE SUBJECT OF FERTILISATION AND CONCLUSIONS.
The essence of normal fertilisation is the union of the egg- and sperm -
cells (p. 156). Normal fertilisation compared with abnormal and with
parthenogenesis (p. 157). Is the essential part of the new organism
contained in the egg-cell alone or in the sperm-cell alone, or in
both ? (p. 158). Why must the nuclei of two germ-cells unite to
effect fertilisation? Twofold purpose of fertilisation (p. 160).
First, to stimulate the production of a new individual. Various
theories regarding rejuvenescence of the organic substance through
the process of fertilisation (p. 161). Second purpose of fertilisation,
to transmit to the offspring the combined properties of both parents
(p. 163). Final significance of the process of reduction (p. 164).
Final significance of the distribution of chromatin at the union of the
germ-nuclei (p. 165). The nuclear chromosomes the chief material
bearers of heredity. Boveri's theory of the ' Individuality ' of
chromosomes (p. 167). Its connexion with Mendel's Law (p. 170).
Object of the combination of qualities effected by the chromosomes
in the process of fertilisation (p. 173). Criticism of Weismann's
views regarding amphimixis (p. 174). The chromosomes probably
are the bearers of the interior laws of development governing organic
life (p. 177).
INTRODUCTORY KEMARKS. AIDS TO THIS INVESTIGATION
EVER since the time of Aristotle the minds of men have
busied themselves with the problem of fertilisation, and with
the way in which the characteristics of the parents are handed
down from generation to generation of their descendants. In
the last few centuries the ovulists and the animalculists have
argued with one another as to whether the ovum or the sperm-
cell was alone, or at least chiefly, responsible for the phenomena
of fertilisation and heredity ; the matter was discussed with
much energy and varying success, and was finally left un-
decided, for neither party possessed the actual knowledge
necessary to enable them to arrive at a decision — it was reserved
for modern microscopical research, with its extremely delicate
and ingenious methods of investigation, to supply a more or less
adequate basis for the solution of these problems. Let us now
consider the results of the most recent research, and see to
what conclusions they lead. It is interesting to observe
that many of the newer theories of fertilisation approximate
very closely to Aristotle's opinion, which was that the female
element supplied the material out of which the new individual
was formed, whilst the male element supplied the impulse
to its development. This coincidence of ideas must not,
however, in any way influence us in judging these theories
critically.
CELL-DIVISION AND HEREDITY 105
During the last few years more new facts have been ob-
served, more experiments made, more theories invented and
published on the problems of fertilisation and its relation to
heredity, than perhaps on any other subject of scientific
research.1 We need not trouble about the purely speculative
theories, but discuss only the scientific material from which the
supports for the theoretical superstructure are taken. We
shall consider the nature of these supports, and see how far
anyone has yet succeeded in uniting them so as to give us any
conception of the structure, which it will be the task of future
generations to complete. But here at once we find ourselves
involved in difficulties. Who is a trustworthy guide in this
investigation ? Who can give us information regarding the
quality of the building materials and the best mode of com-
bining them, so as to form at least the foundation of the future
edifice ? If we take one of the industrious workmen as our
guide, there is some danger lest he show us especially the stones
that he himself has hewn and fashioned, and give us a partial
account of the reasons why these stones must be used in one
way, and not in another. If, on the other hand, we take a
number of the workers as guides, their explanations may
involve contradictions which we cannot solve. If we have
recourse to one of the theorising inspectors, we inevitably
expose ourselves to the risk of falling too much under his
influence and accepting his interpretations, to the neglect of
other, no less well grounded, opinions. Where are we to find
an * impartial expert ' on the subject ?
Of all the recent publications in this department of research
none perhaps is better calculated to give a fair objective
account of it than the ' Allgemeiner Teil ' (General Section) of
Korschelt and Heider's ' Vergleichende Entwicklungsgeschichte
der wirbellosen Tiere ' (* Text-book of the Embryology of
Invertebrates ').2 The authors have not only shown marvellous
industry in collecting and tabulating an immense number of
facts, but they have also displayed great circumspection in
their critical appreciation of the various attempts to explain
these facts theoretically.
1 A list of works on this subject is given by Y. Delage, Korschelt und Heider,
and E. B. Wilson.
2 Part I, Jena, 1902 ; Part II, Jena, 1903. The ' General Section ' has not
been translated into English.
106 MODEKN BIOLOGY
We have frequently referred also to Y. Delage's ' La structure
du protoplasma et les theories sur 1'heredite et les grands pro-
blemes de la biologie generate ' (Paris, 1895). It is of great
importance as enabling us to follow the questions propounded,
although I cannot without reserve accept the author's own
' theorie des causes actuelles.' 1
E. B. Wilson's book, ' The Cell in Development and Inherit-
ance ' (New York, 1902), contains a very good resume of the
phenomena of fertilisation and their connexion with inherit-
ance ; and on this subject I can cordially recommend Oskar
Hertwig's ' Allgemeine Biologie,' Jena, 1906, chapters 11-13.
Much has been done by E. Strasburger3 and J. Eeinke3 to
facilitate a comparison of the results obtained by zoologists
with the analogous phenomena observed by botanists.
I propose to discuss the points of the subject in the following
order :—
1 . What are the problems to be solved ?
2. How do the maturation-divisions of the germ-cells
differ from the ordinary processes of indirect division
of the nucleus ?
3. What is the normal process of fertilisation in an animal
egg, as a result of the union of the egg-cell and sperm-
cell ?
4. In what relation do the phenomena of superfetation in
1 A later edition of the same work was published in Paris, 1903, entitled :
UHeredite et les grands problemes de la biologie generale. A review of the
theories of fertilisation, mixed with a good deal of the hypothetical element,
was given by Delage in his address ' Les theories de la fecondation,' delivered
at the Fifth International Zoological Congress in Berlin (August 1901) and
printed in the Verhandlungen of the same Congress at Jena, 1902 (pp. 121-140).
Cf. also a lecture delivered by Delage in Paris on April 10, 1905, on ' Les
problemes de la biologie ' (Bull, de Vlnstit. general psychologique, V, 1905, No. 3,
pp. 215-236). In an oration at the seventy- third meeting of German naturalists
and physicians in September 1901, entitled 'Das Problem der Befruchtung '
(Jena, 1902), Boveri expounded chiefly his own views on the subject. At
the thirteenth annual meeting of the German Zoological Society in June 1903,
he read a paper on the constitution of the chromatin nuclear substance (' Uber
die Konstitution der chromatischen Kernsubstanz,' Verhandl. pp. 10-33), in
which he developed his views regarding the individuality of the chromosomes.
In the course of this chapter we shall have occasion to refer to the works of
several other scientists. L. Katheriner contributed a good review of the
attempts to solve the problem of heredity to Natur und Offenbarung, 1903,
pp. 513, &c.
2 * Histologische Beitrage,' No. 6 : Uber Reduktionsteilung, Spindelbildung,
Centrosomen und Cilienbildner im Pflanzenreich, Jena, 1900.
3 Einleitung in die theoretische Biologie, chapter 34, ' Morphologic der
Befruchtung.'
GEKM-CELLS 107
animals stand to those of double fructification in
plants ?
5. What are the points of resemblance between the ferti-
lising processes of multicellular animals and plants
and the phenomena of conjugation observed in uni-
cellular organisms ?
6. What light is thrown on the problem of fertilisation
by the facts of natural parthenogenesis ?
7. Experiments in artificial parthenogenesis.
8. Attempts to fertilise non-nucleated fragments of eggs.
9. What conclusions may be deduced from this series of
phenomena with regard to fertilisation in general, and
our knowledge of the material bearers of heredity ?
1. PROBLEMS TO BE SOLVED
What is it that enables living organisms to propagate
their species ? The power of propagation depends upon the
possession of germ-plasm, which is the means of preservation
of species. In unicellular organisms the germ-plasm is contained
in the cell that constitutes the body ; but in multicellular
animals and plants there are distinct germ-cells, out of which
the body of the new individual is formed. The plasm of
these cells, called by Nageli idioplasm and by Weismann
germ-plasm, is therefore the actual bearer of the phenomena
of heredity. Weismann has based upon this fact his well-
known theory of the continuity of germ-plasm.1 He believes
that within the tiny mass of organic substance in the germ-cell,
and especially within its nucleus, are contained the material
constituents for the formation of new individuals, and that
these constituents are transmitted from generation to genera-
tion. He calls these constituents idants, ids, determinants
and biophors, according to their size ; biophors regularly
arranged compose determinants, these form ids (which contain
all the primary constituents necessary to the production
of an individual), and the ids finally combine to make up
idants. This speculation of Weismann's, according to which
germ-plasm is in some degree an extremely delicate, artificial
1 Weismann has given a detailed account of his theory in his lectures on
the evolution theory, 17th lecture (Vol. I, pp. 345, &c., Eng. trans.).
108 MODEEN BIOLOGY
sort of mosaic, is the foundation of his Preformation theory.1
Opposed to this theory are the epigenetic views of 0. Hertwig,
Y. Delage, Hans Driesch and others,3 who believe the develop-
ment of the embryo to be determined, not by material deter-
mining constituents, but by dynamic causes, such as definite
chemical and physical properties of the germ-plasm.3
J. Eeinke has combined with this theory that of Dominants,
which, after the fashion of teleological entelechies, direct and
control the activity of the mechanical energies.4 Driesch
inclines to a similar opinion, as he upholds the autonomy
of the vital processes, and thinks they cannot be accounted
for by mechanical causes.5 All these theories, which I cannot
now discuss in greater detail, have been advanced as supplying
answers to one and the same question : ' How can we explain
the morphological processes, which present themselves to our
consideration, when we observe the phenomena of fertilisation
and heredity in the germ-plasm ? '
A second very interesting question is : 'In the case of the
higher animals and plants, which require the action of both
sexes for their propagation, why is the ovum or the sperm-cell
alone insufficient for embryonic development ? Why is fertilisa-
tion necessary to the development of the ovum ? Is the union
of the two germ-cells, which takes place at fertilisation, essential
to the beginning of embryonic development, or is the object of
it to secure, by means of bisexual propagation (which Weismann
calls amphimixis), the advantages of a twofold inheritance, and
a mixture of the qualities of both parents ? Finally, what
are the real bearers of heredity in the germ-cells ? May we
1 Preformation, because, according to it, every part of the future in-
dividual is formed beforehand, or rather determined beforehand, by means
of most minute determining constituents in the germ-cell.
2 Epigenesis = development through new formations ; according to these
theories the various processes of development in the embryo depend upon
new formations, produced by the joint action of external stimuli and internal
dynamic factors.
3 The problem of determination, i.e. the question whether preformation
or epigenesis lies at the root of organic development, is obviously not limited
to the beginning of the development of the germ, but covers the whole course
of ontogeny (individual development). Cf. Korschelt and Heider, Lehrbuch
der vergleichenden E ntwicklungsgeschichte der wirbellosen Tierc, Part I,
pp. 81-160. The problem of determination will be dealt with more fully in
Chapter VIII, * The Problem of Life.'
4 Reinke, Die Welt als Tat, Berlin, 1903, pp. 275-292 ; also ' Die Dominanten-
Jehre,' in Natur und Schule, 1903, Parts 6 and 7.
5 Driesch, Die organischen Regulationen, Leipzig, 1901.
MATUBATION-DIVISIONS 109
regard the chromosomes of the nucleus as such, and with
what justification ? '
We will now try to examine these questions more closely
from the standpoint of the morphological processes in the
germ-cells, as revealed by the microscope. Even if we fail to
arrive at any final explanation, it is nevertheless important
to see how far scientific research on this subject has advanced.
We must begin with the phenomena of maturation in the
germ-cells.
2. THE MATURATION-DIVISIONS OF THE GERM-CELLS
Both the ovum and the spermatozoon must, before
becoming capable of fertilisation, undergo two divisions, which
are known as maturation-divisions. Let us consider first those
of the ovum.
As Y. Delage rightly remarks, what we generally call a
mature egg, is really the grandmother of the egg-cell. At
that stage the egg is termed a primary oocyte ; after the first
maturation-division it becomes a secondary oocyte, and after
the second division it is an egg capable of fertilisation. This
process of twofold division differs entirely in many respects
from the usual form of division of cell and nucleus, as described
in the preceding chapter. As a rule, the division of a mother-
cell produces two daughter-cells of equal size, and, when they
subdivide, four granddaughter-cells, all of the same size, are
formed ; but the two maturation-divisions of the egg-cell
result in the formation of one large cell, which is the ovum
proper, and of two, or strictly speaking three,1 diminutive cells
or portions of cells, called polar bodies. In the ordinary
course of indirect cell-division a period of rest intervenes
between two divisions, during which period the nucleus
resumes its normal shape ; but there is no resting stage between
the two maturation-divisions ; the second generally takes
place immediately after the first, and for this reason the
separation of the polar bodies from the ovum has been termed
' precipitate cell-division.' Finally, in the normal form of
1 The first polar body often divides again immediately after its separation
from the ovum, so that, when the second polar body is formed, there are in
all three minute bodies present besides the ovum.
110 MODEEN BIOLOGY
karyokinesis, the original number of chromosomes persists in
the daughter-cells ; in maturation-division of the germ-cell,
it is a remarkable fact, that, after the separation of the polar
bodies, the nucleus of the mature germ-cell contains only half
the number of chromosomes that occur in the somatic cells
of the same individual, and at the same time the amount of
chromatin originally in the nucleus is generally reduced to a
quarter. This reduction, but more particularly that in the
number of chromosomes, leads us to speak of the processes of
reduction, which, as will be seen later, appear to be of very
great significance in the problem of fertilisation.
Like the egg-cell, the sperm-cell undergoes a twofold
division in the course of maturation. The primary spermato-
cyte by indirect karyokinesis gives rise to two secondary
spermatocytes, and each of these divides into two spermatids
or ripe sperm-cells, so that in this case, too, the primary sper-
matocyte has four descendants. But whereas the four descend-
ants of the primary oocyte are of unequal size and value, and
only one, the ripe ovum itself, is concerned with fertilisation,
those of the primary spermatocyte are, as a rule, all four of
equal size, each able to fertilise an ovum.1
It is a most important fact that, at the completion of the
processes of maturation, the number of chromosomes in both
sperm and egg-cells is reduced, so that the mature cell contains
only half the number that are present in the somatic cells of
the same individual and of the same species. The bearing of
this fact upon fertilisation will be shown later.3
1 I say ' as a rule,' because Meves believes that he has recently observed
a formation of polar bodies during the maturation-divisions of sperm-cells.
Cf. F. Meves, ' Richtungskorper in der Spermatogenese ' (Mitteil. d. Vereins
Schleswig-Holsteiner Arzte, XI, 1903, No. 6) ; ' Uber Richtungskorperbildung
im Hoden von Hymenopteren ' (Anatom. Anzeiger, XXIV, 1903, pp. 29, &c.).
2 I may incidentally remark that during the maturation-divisions of the
sperm-cells of many animals, and especially of many insects, the presence of
accessory or heterotropic chromosomes has been observed, the use of which
has not hitherto been satisfactorily explained. See Korschelt und Heider,
Lekrbuch der vergl. Entwicklungsgeschichte, &c., 601. R. de Sinety, S.J.,
has traced the history of these accessory chromosomes very carefully in his
Recherches sur la biologic et Vanatomie des Phasmes, Lierre, 1901 ; and so has
Sutton, an American scientist, in his study of a grasshopper (Brachystola
magna). Montgomery gives the accessory chromosomes, discovered by him
in Hemiptera, the name of heterochromosomes. See also Stevens, ' Studies in
Spermatogenesis, with especial reference to the accessory chromosome ' (Carnegie
Institution, Washington, September 1905). E. B. Wilson has recently
published some important articles on the various forms of chromosomes
occurring in Hemiptera, dividing them into idiochromosomes (of which there
MATURATION-DIVISIONS 111
Very various opinions exist as to the time and manner in
which the reduction in the number of chromosomes takes place ;
this may partly be accounted for by the fact that different
scientists have chosen different objects for observation. We
must content ourselves with a condensed summary of the
facts, based chiefly upon Korschelt and Heider (pp. 572,
&C.).1
We must, in theory, distinguish two forms of maturation-
division of germ-cells, viz. those called by Weismann ' equation '
or equal division, and reducing division. The former follows
the ordinary laws of karyokinesis, in which each chromosome
of the mother-nucleus splits lengthwise, thus enabling each
daughter-nucleus to have the same number of chromosomes as
there were in the mother-nucleus, whence this kind of division
is called equal. Eeducing division is altogether different.
When it takes place, whole chromosomes are distributed to
the daughter-nuclei, so that there is a reduction in the original
number of chromosomes, each daughter-nucleus having only
half as many as the mother-nucleus.
When the two- successive divisions of the germ-cell are both
equal, the whole maturation-division is called eumitotic, because
it follows the normal type of mitosis.3 If, on the other hand,
at least one of the two divisions is a reducing division, the
whole process of maturation-division is called by Korschelt
and Heider pseudomitotic, and we may accept this name.
Three varieties of pseudomitotic division must be dis-
tinguished. The reducing division may follow the equal
division, and then we have a case of post-reduction division ;
or the reducing division may precede the equal division,
and then we have a case of pre-reduction division ; or both
are various sizes) and heterotropic chromosomes, and discussing their biological
functions. (' Studies on Chromosomes,' in the Journal of Experimental
Zoology, IT, Nos. 3 and 4, III, No. 1). In the last section of this chapter we
shall refer again to the accessory chromosomes.
1 In one of his recent works, ' Uber die Konstitution der chromatischen
Kernsubstanz,' in the Verhandl. der Deutschen Zoolog, Gesellschafl for 1903,
Boveri describes the statement of the reduction problem given by these
two authors as a 'model.' Cf. also O. Hertwig, Allgemeine Biologie. 1906,
pp. 282, etc.
2 I cannot here discuss the varieties of eumitotic division known as homceo-
typic and heterotypic. In the former a real separation of the two halves of
the split chromosome takes place, in the latter they remain connected by their
ends, so that the two half-loops form a ring. Such chromosomes are termed
' heterotypic.'
112 MODEKN BIOLOGY
divisions may be reducing, and the process may be called
one of double reducing, or a bireduction division.1
These various kinds of maturation-division have a direct
bearing upon the problem when, and how, the original number
of chromosomes in the somatic cells is reduced to half that
number in the egg and sperm-cells at the conclusion of the
process of maturation.
In eumitotic maturation-division, the reduction does not
take place during the divisions, but precedes them. The
primary oocytes and spermatocytes have in this case the
reduced number of chromosomes, before they begin to divide
further. We know absolutely nothing as to the manner in
which this reduction is effected, and very little as to the time
when it takes place. In many plants and animals it seems
to occur very early, during generations of cells preceding the
formation of germ-cells.2
In pseudomitotic maturation-division, the chromatin re-
duction takes place automatically by means of one or both
processes of division, but the manner in which it is effected is
still very obscure, and various authors do not agree in their
interpretation of their microscopical observations.
The actual results obtained stand in the following relation
to the theoretical kinds of maturation-division that have been
described above. The eumitotic type — in which both matura-
tion-divisions are produced by longitudinal splitting of the
chromosomes, so that no reduction in the number of chromo-
somes is caused actually by the divisions — seems to occur very
frequently in both animals and plants. Some authors are
inclined to think that this type might prove to be universal, if
we could explain, in accordance with it, the microscopical
observations that have hitherto been interpreted in the pseudo-
mitotic sense.
Boveri, whose brilliant research work on Ascaris and other
creatures has caused the eumitotic maturation-division to be
known also as the ' Boveri type of division,' emphatically
1 I have ventured to coin this word to designate the double reducing division,
forming it on the analogy of the other names given to division.
2 Cf. Wilson, The CeH,pp. 272, &c., also Strasburger, Uber Eeduktionsteilung,
Spindelbildung, &c., Jena, 1900, pp. 81, &c. Strasburger does not call the
reduced number of chromosomes in the^germ-cells reduced, but original. This
may possibly be correct phylogenetically, but it can scarcely be justified
ontogenetically, at least in the case of multicellular animals.
MATUEATION-DIVISIONS 118
maintains that the reduction in the number of chromosomes
does not take place during the maturation-divisions, nor is it
due to them, but precedes them, inasmuch as in the primary
oocytes and spermatocytes the number of chromosomes is
always half that of the chromosomes in the somatic cells of
the same individual. The Ascaris megalocephala var. bivalens,
chosen by Boveri for investigation, has two chromosomes in
each of its primary germinal vesicles, each consisting of four
grains of chromatin,1 which Boveri believes to have been
formed by a double longitudinal division of the original chromo-
some. This division is prepared in the nucleus of the primary
germ-cells, and is effected by the two maturation-divisions, so
that finally the mature ovum and spermatozoon contain each
two chromosomes in their nucleus, i.e. the same number as
before, whilst the somatic cells contain four.
The eumitotic type of maturation-division of the germ-
cells has been described by many zoologists ; by 0. Hertwig
and A. Brauer (in Ascaris), by Meves, McGregor, Janssens,
Eisen, Carnoy and Lebrun (in Amphibia), Ebner and von
Lenhossek (in the rat), de Sinety (in Orthoptera), &c. Many
eminent botanists, too, and especially Strasburger, with whom
Guignard, Motier and Juel agree, concur in believing the
maturation-divisions of plants to be of the eumitotic type, as
they take place by a twofold longitudinal splitting of the
chromosomes, and these writers are of opinion that the re-
duction in the number of chromosomes is effected before
the maturation-divisions, viz. in the embryo-sac, or at the
formation of the pollen.
Pseudomitotic maturation- division has hitherto been
observed chiefly in Arthropods.
Post-reduction division, in which the first of the two
maturation-divisions is equal, and the second reducing, is
1 It would perhaps be well for this reason to adopt the number 8 for the
chromosomes of the nucleus of the primary germ-cell, as Kathariner has done
in his article in Natur und Offenbarung, 1903, pp. 524, 527. The adoption of
this number would, however, lead to the following difficulties. First, in
Ascaris megalocephala var. bivalens, the primary germ cells would contain
twice as many chromosomes as the somatic cells. Secondly, the twofold
maturation-division would result, not in halving, but in quartering the original
number of chromosomes. I prefer, therefore, to follow Boveri, and regard
the two groups of four grains as only two chromosomes, this number being
half that of the chromosomes in the somatic cells, which is therefore already
reduced.
114 MODEBN BIOLOGY
known also as the Weismann type, as Weismann laid great
stress upon it, although he did so chiefly for theoretical reasons
connected with his theory of heredity. At the maturation
of the eggs of the Copepods among Crustacea, Kiickert and V.
Haecker observed twelve tetrads (groups of four), which, they
believed, split longitudinally at the first division, and trans-
versely at the second, which would then be a reducing division
in Weismann's sense.
Vom Kath described similar phenomena occurring at the
maturation of the egg of the mole-cricket (Gryllotalpa), but,
according to Korschelt and Heider (p. 586), it is still uncertain
whether the second division in this case -is really a reducing
division. With regard to many other insects also in the
last few years the post-reduction division has been frequently
called in question, and it must be observed that the interpre-
tation of the second division as a reducing division is still a
moot point ; for instance, the same microscopical observations
of the maturation of the sperm-cell in Orthoptera led McClung
in 1900 ! to declare the division to be reducing, and de Sinety
(1901 and 1902) to pronounce it to be a double longitudinal
splitting of the eumitotic type.
t The kind of reducing division that I have termed pre-
reduction, in which the reducing precedes the equal division,
has been described as occurring both in spermatogenesis and
oogenesis of animals of widely different types. It was dis-
covered by Korschelt, who observed it at the maturation of
the egg of the annelid Orphryotrocha puerilis, and has been
called after him the Korschelt type. Henking and Paulmier
say that this kind of maturation- division occurs in many
species of Hemiptera, and Montgomery has traced it in other
Hemiptera and in the very obscure Peripatus. On the other
hand, Gross2 declares not the first, but the second, division
to be reducing in the maturation of the sperm-cells of the
Syromastes marginatus, so that this bug would seem to supply
an instance of post-reduction rather than of pre-reduction
division.
1 See also McClung's more recent work, ' The Spermatocyte divisions of
the Locustidae ' (Kansas Univ. Science Bullet., I, 1902, No. 8, pp. 185-231,
with four plates).
2 ' Ein Beitrag zur Spermatogenese der Hemipteren ' ( Verhandl. der Deut-
schen Zoolog. Gesellsch., 1904, pp. 180-190).
MATUKATION-DIVISIONS 115
E. B. Wilson's latest investigations regarding the matura-
tion-divisions of germinal vesicles among Hemiptera l seem to
show that the question of longitudinal or transverse divisions
has lost its primary importance, because the chromosomes
separating at the reducing division were originally distinct,
and were only temporarily united during an intermediate
synapsis stage.3
Montgomery and several other authors ascribe parti-
cular importance to the copulation of chromosomes during
synapsis as facilitating the interchange of qualities be-
tween the chromosomes of the male and female parents
respectively.3
Lastly, bireduction division, in which both maturation-
divisions of the germ-cells are reducing, has been described
by Julin as occurring at the maturation of the egg of an Ascidian
(Styelopsis) , and by Wilcox at that of the spermatozoon of a
grasshopper (Caloptenus), &c. The remark that the interpre-
tation to be assigned to the microscopical observations is by
no means certain, applies to this kind of division even more
than to the others.
Some idea of the difficulties which the student engaged
in this department of research has to encounter, may be
formed from the fact that the chief supporters of the various
division theories have repeatedly changed their minds, and
have assigned to their observations now one interpretation
and now another. I may refer particularly to Boveri and
Strasburger in this respect.
As we have seen (p. 112), Boveri first described the eumitotic
type of maturation-division, which is called by his name, and in
which both divisions are equal and longitudinal, the reduction
in the number of chromosomes having taken place before the
division ; in 1903,4 however, he acknowledged that in a number
of instances an actual reducing division takes place, ' though
not precisely in Weismann's sense.' Now he thinks that only the
1 * Studies on Chromosomes ' (Journal of Experimental Zoology, II, III,
1905, 1906). Cf. also p. 110, note 2.
2 On the subject of this stage see Pantel and de Sine~ty, ' Les cellules de la
lignee male chez le Notonecta glauca ' (La Cellule, XXIII, 1906, fasc. I, pp.
89-303), pp. lll,&c.
3 See 0. Hertwig, Allgemeine Biologie, pp. 291, 292.
4 Boveri, ' Uber die Konstitution der chromatischen Kernsubstanz ' (Ver-
handl. der Deutschen Zoolog. Gesellsch., 1903, pp. 10-32), p. 27.
i 2
116 MODEBN BIOLOGY
first division is longitudinal, and he believes the second to be
transverse, effecting a reduction in the number of chromosomes.
If this is true, we have post-reduction division, approximating
to the Weismann type.
In 1904 Strasburger,1 the botanist, abandoned his earlier
opinions regarding the eumitotic type of maturation. His
most recent investigations of the pollen-mother-cells of Galtonia
show the first of the two maturation-divisions of the chromo-
somes to be transverse, resulting in a reduction of their number ;
the second, on the contrary, appears to be a longitudinal or
equal division. In 1904, therefore, Strasburger, it would seem,
upheld, instead of the eumitotic type, the pseudomitotic, in
the form of a pre-reduction division, corresponding to the
Korschelt type. But we should have almost as much justifi-
cation for speaking of post-reduction in this case ; for, as
Strasburger expressly states, the longitudinal division, which is
actually the second in order of occurrence, is anticipated by
a longitudinal splitting of the chromosomes, which precedes
the first transverse division. In 1905, however, Strasburger
returned to his earlier opinion regarding the eumitotic type
of maturation-divisions,2 and he now again maintains that
both divisions are longitudinal and equal, and that the real
reduction in the number of chromosomes precedes them.
He agrees, therefore, now with Abbe V. Gregoire, who expressed
similar views in 1905.3
The theory of eumitotic maturation-division seems, there-
fore, to have triumphed over that of pseudomitotic.4 Whether
inthechromatin skein or spireme, formed before the maturation-
divisions take place, the individual chromosomes are joined
longitudinally or by their apex, is a question raised by Boveri
in 1903, and discussed by Gregoire, Strasburger, Schreiner5
1 Strasburger, ' Uber Beduktionsteilung ' (Sitzungsber. der Berl. Akademie
der Wissensch., XIV, 1904, pp. 587-614).
1st,, JLJLHsU/rl't'tVy ^VJ-JJ-J-j J. t/VcJj i Cl/1 U J.y KMr* x — * A /*
V. Gregoire, ' Les resultats acquis sur les cineses de maturation dans lea
regnes ' : I. memoire : Revue critique de la litterature (La Cellule. XXII,
2 Strasburger, ' Typische und allotypische Kernteilung ' (Jahrb. fur wissen-
schaftl Botanik, XLII. 1905, Part I, pp. 1-71).
3 V.
deux
1905, fasc. 2, pp. 221-374).
4 Cf . J. Marechal, ' Uber die morphologische Entwicklung der Chromosomen
im Selachierei und Teleostierei ' (Anatom. Anzeiger, XXV, 1904, pp. 383-398
and XXVI, 1905, pp. 641-652).
5 A. and K. E. Schreiner, ' Neue Studien iiber die Chromatinreifung der
Geschlechtszellen ' (Archives de Biohgie, XXII, 1906, fasc. I, pp. 1-69).
MATUEATION-DIVISIONS 117
and Bonnevie,1 but we cannot consider it fully now. The
first view is probably the correct one. I may remark inci-
dentally that almost all the recent results of the examination
of chromosomes tend to confirm Boveri's theory of their
' individuality.' But I shall recur to this theory in the ninth
section of this chapter.
J. Gross 3 has recently summed up the results of his inves-
tigations into the maturation-divisions of the germ-cells in the
following sentence : ' The most important results of cytological
research into the problem of reduction in the last few years seem
to me to be two : it has been demonstrated that a real, qualita-
tive reduction actually takes place, and it has been found that a
conjugation of the chromosomes of both parents as a rule
precedes the maturation-divisions.'
I have already dwelt too long upon the various theories
connected with the maturation of the germ-cells. The accom-
panying diagrams will enable the reader to form some idea
of the maturation of the egg-cell and of the formation of the
polar bodies ; they represent the particular kind of division
that I have termed post-reduction. It must, however, be
observed that these are merely diagrams, and do not represent
the actual process ; they have been designed to show, in the
simplest way possible, the first division as equal, and the
second as reducing.
Let us assume the primary oocyte to have four chromosomes
in its nucleus before the process of division begins. The first
stage in the process is that the germ-nucleus or vesicle moves
towards the periphery of the cell (fig. 17). Then the chromo-
somes of the nucleus arrange themselves in the manner de-
scribed in Chapter V (p. 94), so as to form an equatorial plate
or crown in the middle of an achromatic nuclear spindle
(fig. 18) ; they split longitudinally, and the daughter-chromo-
somes withdraw to the poles of the nuclear spindle (fig. 19).
This first nuclear division is an equation or equal division of
the ordinary kind, not a reducing division. The upper group
of four chromosomes with the centrosome of the egg-cell
1 ' Untersuchungen iiber Keimzellen : I. Beobachtungen an den Keimzellen
von Enteroxenos Oestergreni ' ( Jenaische Zeitschr. fur Naturwissensch., XLI,
1906, part 2, pp. 229-428).
2 ' Uber einige Beziehungen zwischen Vererbung und Variation ' (Biolog.
Zentralblatt, 1906, Nos. 13-15, &c., p. 396).
118
MODEEN BIOLOGY
belonging to them is now forced against the periphery of the
cell, until it finally passes out of the cell, surrounded by a
small quantity of protoplasm (fig. 20). This forms the first
polar body (rl in fig. 20). Meantime, a fresh nuclear spindle
forms immediately round the four chromosomes left in the
egg-nucleus (fig. 20) ; but this time there is no longitudinal
FIG. 17.
FIG. 18.
FIG. 19.
FIG. 20.
FIG. 21.
FIG. 22.
FIGS. 17-22. — Diagrams representing the maturation-divisions of the egg-cell.
r^= first polar bo<j|T; r"— second polar body; vk~ female pronuclcus.
splitting of the chromosomes. They arrange themselves in
pairs (fig. 21) ; the upper pair approach the periphery of
the cell, and are expelled from it with a particle of protoplasm,
and so form the second polar body (r- in fig. 22). This
second division was reducing, for the nucleus of the egg-cell,
which now resumes its original shape, and at this stage is
called the female pronucleus (v~k in fig. 22), now has only two
chromosomes instead of four. If, in the meantime, the first
polar body has again divided (n in figs. 21 and 22), the
THE PKOCESS OF FERTILISATION 119
result of the two maturation-divisions of the egg-cell has been
the production of one large and three small cells, of which only
the first, the egg-cell prepared for fertilisation, is of interest
for us.1
3. THE NORMAL PROCESS OF FERTILISING IN AN
ANIMAL OVUM
(See Plate I)
Let us now turn to the process of fertilisation in its normal
form in animal ova, as microscopical research has revealed it
to us. 0. Hertwig was the first to succeed, in 1875, in lifting
the veil that for so many thousands of years had rested over
these phenomena. In the course of observations on the
eggs of the sea-urchin (Echinus), he saw that during fertilisation
a thread-like sperm-cell passes into the ovum ; the head of
the sperm-cell changes into a so-called male pronucleus, and
unites with the nucleus of the ovum, or female pronucleus.
This union of nuclei results in the normal process of fertilisation,
for it gives rise to the cleavage-nucleus of the fertilised ovum,
which at once begins to divide by means of the nuclear
spindle of the cleavage-nucleus, so forming the first pair
of cleavage-corpuscles, or blastomeres, from whose further
divisions all the tissues and organs of the new individual
are produced.
At first sight the process of fertilisation thus described
seems very simple, but it becomes very complex by reason
of the vast varieties in its details, in the case of different plants
and animals. Moreover, very various opinions still prevail as
to the parts played by the cell-nucleus, the centrosome, and the
egg-plasm respectively in the work of fertilisation. Korschelt
and Heider devote over one hundred pages to a description
of these phenomena in their ' Vergleichende Entwicklungs-
geschichte der wirbellosen Tiere ' (Allgemeiner Teil, pp. 628, &c.).
I must obviously limit myself to what is absolutely necessary
1 For the subsequent history of the polar bodies (globules polaires) and their
importance, see Korschelt and Heider, Lehrbuch der vergl. Entwicklungsgesch.,
pp. 549, &c. They discuss Petrunkewitsch's theory that the polar bodies
continue to exist and supply the material for the germinal glands of the
future embryo. But nothing is known with certainty on the subject-
120 MODEKN BIOLOGY
in order to enable my readers to form some idea of the essential
processes of fertilisation and heredity.
Although the ovum of the Echinus measures only ^ mm.
in diameter, it is, like all other ova, of enormous size in com-
parison with the spermatozoon — and this is especially true
in the case of eggs containing much yolk. Such eggs have
stored up in their egg-plasm a considerable quantity of
nutritive matter, which is used in the development of the
future embryo. The sperm-cells, on the contrary, are some of
the smallest cells occurring in living organisms,1 for their
sole task is to penetrate the ovum and fertilise it. For this
reason the protoplasm that constitutes the cell-body is generally
only a thread-like flagellum, which serves as an organ of
locomotion, and the thickened head is the nucleus of the
sperm-cell ; between head and tail is the so-called middle-
piece containing the centrosome of the sperm-cell.
In spite of the extraordinary difference in size and shape
between the ovum and the spermatozoon, their nuclei are so
far of absolutely equal value, for they contain the same number
of chromosomes. Both the male and the female pronuclei
contain half the number of chromosomes found in the somatic
cells of the same species. This fact, to which I referred in
speaking of the maturation-divisions of the germ-cells, is of
great importance in our consideration of fertilisation and
heredity.
The union of the male and female pronuclei to form the
cleavage -nucleus of the fertilised ovum does not necessarily
involve a real fusion of the nuclei ; on the contrary, in many
cases the nuclei with their chromosomes remain distinct from
one another, though they take up their positions close together,
so as to form a common cleavage-spindle. We may follow
Korschelt and Heider (p. 682) in distinguishing two chief types
of fertilisation. The first is the so-called Echinus-type, deriving
its name from the sea-urchin (Echinus), in which it was first
observed and described by 0. Hertwig (1875-1878). In this
type the two pronuclei actually fuse together to form one
resting cleavage-nucleus, which does not begin to divide until
the fusion is complete. It should be noticed, however, that
1 In mammals they often measure (without the tail filament) only 0*003 mm.
See R. Hertwig, Lehrbuch der Zoologie, 1905, p. 49 (Eng. trans, p. 60).
THE PKOCESS OF FEBTILISATION 121
the chromosomes of the two pronuclei do not fuse together,
but come into close juxtaposition. The second type is the
Ascaris-type, deriving its name from the maw-worm of the
horse (Ascaris megalocephala), in which it was observed by E.
van Beneden in 1883 ; l in it the two pronuclei remain indepen-
dent, but take up their position close together, so as to produce
the first cleavage -spindle in common. Having produced it,
they break up, and distribute their chromosomes by longitu-
dinal division to the two daughter-nuclei. Many instances
of both types of union occur in the animal kingdom, in very
various families and classes, and also in closely related species ;
in fact Boveri (1890) and Klinckowstrom (1897) have found
them even within one and the same species.
I have chosen the second type to illustrate the normal
phenomena of fertilisation, because it has the advantage ,of
showing more clearly how the paternal and maternal chromo-
somes are evenly distributed at the cleavage of the fertilised
ovum. In a lecture on the subject of fertilisation (' Das
Problem der Befruchtigung,' Jena, 1902), Boveri sketched the
process on the lines of the Ascaris-type, illustrating it by
diagrams, which are reproduced on Plate I, figs. 1-7. 2
The egg-nucleus is coloured blue and the sperm-nucleus
red, in order to make it easy to distinguish the two nuclei and
the chromosomes of the cleavage-spindle proceeding from them.
The nucleus of the mature egg-cell, which after the matura-
tion-divisions is called the female pronucleus, moves from the
excentric position, occupied during the formation of the
polar bodies, back into the centre of the cell (Plate I, fig. 1).
Meantime a spermatozoon has made its way into the ovum (at
the top of fig. I).3 Only its head and middle-piece, however,
1 This type was perhaps observed by 0. Hertwig between 1875 and 1878 as
occurring in Mitrocoma and Aequorea (Korschelt and Heider, p. 681).
2 I say ' on the lines of the Ascaris-type,' because in many details this sketch
is at variance with actual observations made by E. van Beneden, 0. Hertwig,
Carnoy, Boveri, &c., on Ascaris megalocephala var. bivalens. It should be
noticed particularly that in Ascaris the spermatozoon does not lose a tail,
but the whole sperm-cell, which in this case is conical, passes into the egg-
plasm. Cf. also E. Korschelt, * Uber Morphologic und Genese abweichend
gestalteter Spermatozoon ' (Verhandl der Deutschen Zoolog. Gesellsch., 1906,
pp. 73-82).
3 Circumstances vary greatly in different cases. In some animals the
maturation-divisions of the egg precede the entrance of the spermatozoon,
in others they are simultaneous with or subsequent to it. Cf. Korschelt and
Heider, pp. 630-632.
122 MODEEN BIOLOGY
really enter it ; the tail filament, representing the protoplasmic
body of the sperm-cell, is generally thrown off, or it is quickly
resolved in the protoplasm of the egg-cell. The head and
middle-piece of the spermatozoon rotate through 180°, so
that the middle-piece, which was previously behind the sperm-
head, is now in front of it ; the spermato-centrosome, or cen-
trosome of the sperm-cell, contained in the middle-piece, now
becomes visible, and sends out a ring of protoplasmic rays
(fig. 2), the so-called ' sperm-aster,' which is here represented
as small, although it often stretches over the greater part of
the egg. A very remarkable transformation of the sperm-
head now begins. It swells up — in consequence, as Y. Delage
thinks, of taking in water from the egg-plasm — and, as it swells,
it reveals its nuclear character by forming a chromatin frame-
work (Plate I, figs. 3 and 4), until finally it appears as a male
pronucleus (fig. 5), exactly equivalent to the female. Mean-
time the spermato-centrosome has undergone a series of
further modifications. It divides (Plate I, fig. 3) ; the two
half-centrosomes take up a position on either side of the two
nuclei (fig. 4) and develop their astrospheres (fig. 5). The
chromatin substance of the two pronuclei, now in close proxi-
mity, next proceeds to transform its chromatin framework,
in readiness for the first cleavage of the egg-cell. Each pro-
nucleus develops the same number of chromatin loops, which
usually resemble one another exactly in size and shape. In
the diagram (fig. 6), which might be taken as representing the
fertilisation of the maw-worm of the horse, Ascaris megalo-
cephala var. bivalens, each pronucleus contains two chromatin
loops or chromosomes, i.e. half the number contained by the
somatic cells of the same animal. The cleavage-spindle is next
formed ; it gives rise to the first division of the fertilised egg-
cell, and .so to the first stage in the development of the future
embryo.
Each of the two chromosomes in the parent nuclei splits
lengthwise into two parts, which arrange themselves in the
middle of the nuclear spindle formed by the centrosomes
(fig. 7). Then the four daughter-chromosomes on the left,
two being paternal and two maternal in origin, move to the
left pole of the spindle ; the corresponding four on the right
move to the right pole of the spindle, and at the two poles they
THE PKOCESS OF FEKTILISATION 123
give rise to the two daughter-nuclei of the first cleavage-cells
(blastomeres) of the embryo. Thus each of the first two daughter-
cells contains four chromosomes in its nucleus, two from the
father and two from the mother. Hence it comes about that
each of the cells in the embryo, which are produced by continued
indirect karyokinesis from the fertilised ovum, contains an
equal number of paternal and maternal chromosomes, and the
total number is equal to that of the chromosomes in the
somatic cells of the parents, and double that contained in
either the male or female pronucleus. It would seem, therefore,
that by this process a precisely equivalent transmission of the
nuclear elements of both parents is secured to their offspring.
We must here refer to an observation, made originally by
Boveri in 1887 l and confirmed by subsequent study of Ascaris
megalocephala, which, whilst, to some extent, modifying the
account just given, lends it additional weight in its bearing
upon the question of transmission. In Ascaris; in all the
cleavages from the two-cell stage onwards, the cells of the
germinal area of the embryo present characteristics in their
nuclei and processes of karyokinesis distinguishing them from
the somatic cells of the same embryo. Only the cleavage-
granules destined to give rise to the germ-cells preserve the
original chromosomes, which they receive from the fertilised
egg-cell, in unaltered form ; the cleavage-granules destined to
produce the somatic cells, as soon as they begin to divide,
reject the thickened ends of the chromosomes, and the rest of
the chromatin loop breaks up into a number of smaller pieces,
that subsequently reappear. Boveri called this phenomenon
' chromatin diminution,' and it seems to show that only in the
germ-areas is the continuity of the germ-plasm fully main-
tained, whilst many divergencies may occur in the tracts of
somatic cells.3
It is a fact that individuals, born of the same parents,
differ to a certain extent both from their parents and from one
another, and it is no less true that the qualities of grand-
parents or of their collateral relatives, latent in the generation
1 Cf. Korschelt and Heider, pp. 151, 152.
2 For further evidence in support of this theory, see Boveri, ' Uber die
Konstitution der chromatischen Kernsubstanz,' pp. 18-20 (VerhandL der
Deutschen Zoolog. Gesellsch., Wurzburg, 1903, pp. 10-33). Cf. also 0. Hertwig,
Attgem. Biologic, 1906, pp. 199-201).
124
MODEEN BIOLOGY
next in succession, reappear suddenly in the grandchildren.
Boveri's microscopical observations, to which we have referred,
may be taken as corroborating the theory that the chromatin
elements of the nucleus are the means of transmitting heredi-
tary properties. There is, therefore, actual evidence in support
of the theory held by Eoux, Strasburger, 0. and K. Hertwig,
Weismann, Kolliker, Boveri, &c., that in the chromosomes of
FIG. 23. — Transverse section of the blastula stage of an embryo of
Ascaris megalocephala var. bivalens.
the nucleus we may discover the real substance of heredity,
which Nageli calls idioplasm.
In order to illustrate the differentiation of the germ-cell
area from the somatic-cell area in the case of Ascaris megalo-
cephala var. bivalens, I give, in fig. 23, an exact microscopical
reproduction of a transverse section of the embryo of this
creature at the blastula stage.1
1 The figure is taken from a long series of sections, stained with Heidenhain's
iron-haematoxylin, showing the maturation-divisions and the processes of
fertilisation and development in Ascaris megalocephala. The series was
prepared by my colleague, K. Frank, S.J., under Heider's direction. In the
original the centrosomes at the two ends of the cleavage -spindle in cells c and d
can be seen more plainly than in the reproduction ; they seem to be little
circular formations marked off from the surrounding plasmic rays.
FEKTILISATION AND HEKEDITY 125
The two uppermost cells, a and b, are two somatic cells
with resting nuclei, in each of which two dark spots, nucleoli,
can be plainly seen. The two middle cells, c and d, are like-
wise two somatic cells, but they are still in the act of mitosis ;
the fine chromatin rods, still grouped about the equatorial
plate in the centre of the plainly visible achromatic nuclear
spindle, are actually in process of division. Also the centro-
somes with their astrospheres at the two poles of the spindle
are shown very beautifully. Hence this illustration serves
to supplement the formal diagrammatic representation given
in Chapter V of the process of indirect nuclear division (see
p. 95). The lowest cell, e, with its four large chromatin-loops,
represents, according to Boveri, one of the germ-cells in the
embryo. There is a great difference between the chromosomes
in it and those in the somatic cells, and the fact that the future
germ-cells contain much more chromatin than the somatic
cells, is an argument in favour of the theory that the chromo-
somes of the nucleus are the bearers of heredity. We do not
yet know how the normal number of four chromosomes, which
subsequently are present in the somatic cells of Ascaris, arises
out of the numerous chromatin rods of the somatic cells c and d.
Let us now refer again to the account already given of
the process of fertilisation in the Ascaris-type. This, and the
EMnus-iype, which differs from it by the formation of one
cleavage-nucleus, both show us that, in the first place, fertilisa-
tion leads to the beginning of the embryonic development of a
new individual, because it causes the cells to divide ; in the
second place, it restores the normal number of chromosomes
for all the somatic cells of the new individual ; and lastly
it distributes to every cell of the embryo, as an inheritance, an
equal number of chromosomes derived from each parent.
The last two facts taken in conjunction show the bearing
of fertilisation upon heredity ; the first shows its bearing upon
germinal development.
As I shall have to discuss the theoretical value of these
phenomena at the close of this chapter, it must suffice for
the present thus briefly to indicate the twofold object of
fertilisation.
I Before passing on to other points connected with the
problem of fertilisation, I must once more refer to the normal
126 MODEKN BIOLOGY
process as already described and as illustrated by Boveri's
diagrams (Plate I, figs. 1-7). We may ask : ' What is it
in this case that gives rise to the formation of the cleavage-
spindle, and thus to the first division of the ovum, which con-
stitutes the starting point in the development of the embryo ? '
The impulse proceeds from the male centrosome, which pene-
trates into the ovum with the middle-piece of the spermatozoon.
In the course of the preceding maturation-divisions the centro-
some of the egg-cell either is lost or degenerates, and conse-
quently, in spite of possessing a great quantity of nutritive
plasm, the egg-cell is incapable of further division, for, in losing
its centrosome, it has lost its kinoplasm, as Strasburger calls
it, the active motorplasm in the cell. It requires, therefore, a
new * organ of division ' before it can proceed to embryonic
development, and this organ of division is, in normal fertilisa-
tion, the centrosome of the sperm-nucleus. Its division gives
rise to the two centrosomes (Plate I, figs. 2-6) which form the
poles of the. first cleavage-spindle (Plate I, fig. 7) and cause the
chromatin loops of the united male and female pronuclei to be
distributed evenly between the first two cleavage-nuclei of the
fertilised ovum.
This account of the process of fertilisation was first given
by Boveri in 1887 ; l according to it, the impulse giving rise to
embryonic development is not supplied by the union of the
two pronuclei, but is the primary object of the fertilisation
caused by the introduction of the sperm-centrosome into the
ovum. The union of the pronuclei is the secondary object,
and produces the transmission of the qualities of both parents
to the offspring, but, according to this view, it is only a result
of the action of the male centrosome upon the protoplasm of
the female egg-cell.
As Boveri himself is careful to state,2 this account of the
process of fertilisation is not universal in its application ;
it cannot be applied to all forms of fertilisation in animals and
plants, but only to those of most multicellular animals ; 3 for
1 ' tiber den Anteil des Spermatozoons an der Teilung des Eis ' (Sitzungs-
bericht der Gesellsch. jiir Morphol. u. Phys,, Munich, III).
2 Das Problem der Befruchtung, pp. 23, &c.
a According to Wheeler the centrosome of the ovum remains in Myzostoma,
and forms the poles of the cleavage-spindle. Cf. Korschelt and Heider,
p. 657.
SUPEKFECUNDATION AMONG ANIMALS 127
hitherto no centrosome has been observed at the fertilisation
of the higher kinds of plants,1 nor at the conjugation of uni-
cellular animals.
In natural parthenogenesis the development of the ovum
takes place without fertilisation by a male germ-cell, and so no
spermato-centrosome occurs, therefore it is not essential to
give rise to the embryonic development of the egg. Eecent
experiments in artificial parthenogenesis have succeeded, by
means of various mechanical, thermal, chemical or other
stimuli, in causing centrosomes to form, and the subsequent
cell-division to take place, in the unfertilised eggs of animals,
in which, under normal circumstances, the male centrosome
supplies the cell with the means of division. We must therefore
be careful, even in the normal fertilisation of animal ova, not
to ascribe to the spermato-centrosome too much influence in
setting up embryonic development in the ovum.
We can thus appreciate the reasons which led so great an
authority on the problem of fertilisation as B. Hertwig to con-
tent himself with the simple statement that ' the essential
feature of fertilisation consists in the union of egg- and sperm-
nuclei ' (Lehrbuch der Zoologie,' p. 124 : Eng. trans, p. 149).
4. THE PHENOMENA OF SUPERFECUNDATION AMONG ANIMALS
AND DOUBLE-FERTILISATION IN PLANTS
Under normal conditions during the process of fertilisation
only one sperm-cell penetrates an animal ovum, although there
may be hundreds in its immediate neighbourhood. In many
eggs this is secured by the construction of the enclosing mem-
brane, which allows spermatozoa to enter at one point only.
In the case of eggs with no such point of entrance (micropyle)
the same result is attained in another way — a vitelline mem-
brane forms immediately after the entrance of one spermatozoon,
excluding all others. If the reacting power of the egg be
weakened by means of strychnine, or other poison, so that
it admits several spermatozoa, a normal development never
results ; the numerous centrosomes carried into the egg give
rise to the formation of karyokinetic figures with several poles,
or of very large nuclei which divide irregularly and lead to an
1 Cf. Chapter V, p. 99.
128 MODEEN BIOLOGY
abnormal process of cleavage and to the speedy death of the
embryo. Hence Boveri was right in stating emphatically
in 1902 that the entrance of two spermatozoa ruins a perfectly
normal egg. The explanation of this fact is that the intro-
duction of several centres of division into the egg hinders its
normal development.
In many animals, however, exceptional cases have been
observed when several sperm-cells have entered one egg under
normal conditions. (Gerard, 1901.) But, when this occurs,
only one sperm-nucleus unites with the egg-nucleus, and the
rest are absorbed by the egg-plasm. In 1902 Boveri 1 ob-
served these processes in sea-urchins' eggs, fertilised with
two spermatozoa, and he applied the results of his observations
very ingeniously to his investigations into the nature of the
nucleus and the importance of the chromosomes.
We must distinguish the above-mentioned pathological
superfecundation from what is called physiological polyspermy,
which recent research has proved to occur in many kinds of
animals. In this case also only one sperm-nucleus unites with
the egg-nucleus to form the first cleavage-spindle, but, as
Kiickert, Oppel, Samassa (1895), and Nicolas (1900) have ob-
served, especially in the eggs of Selachii and reptiles, only a
few of the other nuclei perish — many of them are transformed
into the so-called merocytes or yolk-nuclei of the embryo ; not
much is known with certainty about their subsequent fate, but
they are supposed to be connected with the vegetative functions
of the egg, and to expedite the division of the abundant vitelline
substance.
Closely related to physiological polyspermy among animals
is double-fertilisation, an interesting phenomenon occurring in
Angiosperms among the higher plants. A good deal of light
has been thrown on this subject and on its biological signifi-
cance by Nawaschin (1898), Guignard (1899 and 1901), and
Strasburger (1900).3
In this process two sperm-nuclei penetrate into the embryo-
1 * tiber mehrpolige Mitosen als Mittel zur Analyse des Zellkerns ( Ver-
handl, der physikalisch-medizinischen Oesellsch., Wiirzburg, XXXV, pp. 67-90).
2 For a good summary of works published before 1900, and dealing with
the phenomena of double- fertilisation, see G. Richen, S.J., in Natur und Offen-
barung, 1900, pp. 561, &c. Cf. also Korschelt and Heider, Lehrbuch der vergl.
Entwicklungsgeschichte, p. 696.
DOUBLE-FERTILISATION IN PLANTS 129
sac, one of which unites as the male pronucleus with the egg-
nucleus, thus forming the cleavage-nucleus of the mother-cell
of the embryo. The other amalgamates with the secondary
nucleus of the embryo-sac (formed by the union of the two
polar cells), or in some cases with one of the polar cells
before their union, and thus produces the nucleus of the
mother-cell of the endosperm, which has to supply nourish-
ment to the embryo. It is a remarkable fact that one of the
two sperm-nuclei has a generative, and the other a vegetative
function to discharge.
This double fertilisation in Angiosperms is of importance
in explaining some mysterious phenomena in heredity, the
so-called xenia. J. Reinke says on this subject : l 'It was
known from earlier observations that if ripe heads of white-
or yellow-grained maize (Zea Mays) were dusted with pollen
from the blue- or brown-seeded variety, blue or brown seeds
might occur, or the yellow seeds might be speckled with blue
or brown spots. Focke gave the name of xenia to this pheno-
menon. It became easy of explanation after the discovery
of double-fertilisation, and de Vries and Correns have proved
that when maize is dusted with the pollen of another variety,
not only the embryo, but also the endosperm, shows hybrid
properties.'
A remarkable contrast to normal polyspermy is displayed
by the specific polyembryony of certain parasitic Hymenoptera.
According to Silvestri,2 from one single egg of Litomastix
truncatellus are produced about a thousand sexed and some
hundreds of sexless larvae. One spermatozoon suffices to
bring about this extraordinary productiveness in the fertilised
egg, and even the unfertilised eggs, which need no spermatozoon,
show the same complicated result of their parthenogenetic
development. We have here one of the strangest riddles of
life, that seems to be in direct conflict with the theory of the
individuality of the chromosomes, but future generations may
succeed in solving it.
1 Einleitung in die theoretische Biologie, p. 440.
* Un nuovo interessantissimo caso di germinogonia (Poliembrionia
specified), &c.' (Rendiconti delta E. Accademia dei Lincei, Classe d. scienze
fisiche, &c., XIV, 1905, pp. 534-542) ; ' Contribuzione alia conoscenza biologica
degli Imenotteri Parassiti,' I. ' Biologia del Litomastix truncatellus, ,' Portici,
1906 (Estr. d. Annali delict E. Scuola Sup. d'Agricoltura di Portici, VI). •
K
130 MODEEN BIOLOGY
5. CONJUGATION IN UNICELLULAR ORGANISMS AND ITS
BEARING UPON THE PROBLEM OF FERTILISATION
In order to understand the importance of the union of
germ-cells in the normal processes of fertilisation in higher
plants and animals, we shall do well to compare them with
similar processes in the lowest forms of organic life. Let us
begin with the conjugation of Infusoria.
The Ciliata have two nuclei, both containing chromatin,
but one — the macronucleus — is larger than the other — the
micronucleus. As Biitschli showed, only the micronucleus
takes an active part in conjugation, so that it may be called
the sexual nucleus. The macronucleus disappears before
conjugation ; its activity is limited, therefore, to the period
between two acts of conjugation, when the ordinary vital
functions are performed, and it may be called the assimilation
nucleus, which controls the processes of feeding and movement.
The multiplication of these tiny Ciliata takes place as a rule
by simple division, so that one mother-cell splits into two
daughter-cells. This process begins with indirect division
of the micronucleus, which forms a spindle ; it is only later
that the macronucleus divides directly by way of elongation and
constriction, and then the cell-body divides. The micronucleus
reveals its character as the real sexual nucleus even at this
period, but it does so more clearly in the course of conjugation.
The power possessed by Infusoria of multiplying by
division is not unlimited ; the periods of division are interrupted
from time to time by the sexual phenomena of conjugation,
by means of which, as in the processes of fertilisation amongst
higher animals, a reorganisation of the living substance is
effected.1 According to K. Hertwig and Maupas the con-
jugation of Ciliata (e.g. in Paramaecium) takes place in the
following way.2
1 See R. Hertwig, ' Uber Wesen und Bedeutung der Befruchtung '
(SitznngsberichtederA'kad.der Wissenschaften,Munich, XXXII, 1902, pp. 57-73).
2 B. Hertwig, ' Uber Befruchtung und Konjugation ' ( VerhandL der
Deutschen Zoolog. Gesellsch., 1892, pp. 95-112) ; also Lehrbuch der Zoologie,
1905, p. 182 (Eng. trans, p. 206); Maupas, ' Recherches experimentales
sur la multiplication des Infusoires cilies ' (Archives de Zoologie experimentale
et generate, VI, pp. 165-277) ; see also Weismann, Evolution Theory, Vol. I,
pp. 319, &c., with fig. 85 (Eng. trans.) ; 0. Hertwig, Allgemeine Biologic,
1906, pp. 294, &c.
CONJUGATION IN UNICELLULAR ORGANISMS 131
Two individuals take up a position close to one another,
and whilst the macronucleus breaks up, the micronucleus
becomes active. In each individual it becomes spindle-
shaped, and then divides twice in succession, so that each
creature now possesses four spindles. Of these, three, which
are called secondary spindles, gradually degenerate, thus
recalling the polar bodies expelled from the egg-cell. The
chief or primary spindle remains, and again divides into two,
one of which, called the female spindle, remains in each
individual, whilst the other, called the male spindle, passes
into the adjacent animal, and fuses with its female spindle.
The result of their union is to produce in each animal a single
new division-spindle, which gives rise to the copulation-nucleus,
and its development completes the conjugation. The copula-
tion-nucleus corresponds to the cleavage-nucleus of the fertilised
ovum ; when it divides it forms the macronucleus and the
micronucleus of the regenerated individual, which now moves
away from its neighbour.
We cannot here discuss in detail all the differences between
the phenomena of conjugation and the processes of fertilisation.
A comparison of them shows them to be identical in principle.
The conjugation of two Infusorians aims at forming in both
individuals a new copulation-nucleus, which is made up of the
chromosomes of the micronucleus of each in equal proportions.
It is, therefore, a cross fertilisation, agreeing in its essential
points with the processes of fertilisation in multicellular
animals and plants, and showing that the laws, to which we
have seen that they conform, are applicable also to unicellular
organisms. It may be mentioned further that in many
Cryptogams (Fucus, Peronospora) the phenomena of conjuga-
tion still more closely resemble the processes of fertilisation
in higher organisms.
In the phenomena of conjugation in unicellular animals
and plants, we can actually trace the stages of a gradual
approximation to the differentiation of male and female
germ-cells, which finds its complete expression in the fertilisa-
tion of higher animals and plants.1 The two specimens of
1 On this subject see also Y. Delage, ' Les theories de la fecondation,' 1902,
pp. 122, 123 (Verhandl. des V. internal. Zoologenkongresses, pp. 121-140). The
bearing of this series upon the history of evolution is, however, as Delage
K 2
132 MODEEN BIOLOGY
Paramaecium, whose conjugation has just been described, were
exactly similar to one another both before and after their
conjugation. The same may be said of the daughter-indi-
viduals, formed by the subsequent division of the regenerated
specimens ; each can in its turn enter into conjugation with
another of its own kind. There is, therefore, no difference at
all in the sex of the cells uniting in conjugation. We might
say the same of the Noctiluca miliaris, that causes the phos-
phorescence of the sea,1 and of many other Infusorians. If, on
the other hand, we consider another Infusorian, Vorticella
nebulifera, we find a remarkable difference in the conjugating
individuals ; one of them, the macrogonidium, is larger and
represents the egg-cell, whilst the other, the microgonidium,
is smaller, and represents the spermatozoon. In one plant,
Fucus platy carpus, belonging to a low Order, we find a still
more complete sexual differentiation of the conjugating
individuals ; round one relatively enormous spherical egg-
cell swarm numerous diminutive spermatozoa destined to
fertilise it.
We can trace a distinct advance towards sexual differentia-
tion in the case of those Infusorians, which form what are
called colonies, consisting of groups of cells, each being a
separate individual.3
In Pandorina morum sixteen unicellular individuals unite
to form a colony, and, at the time of sexual reproduction,
change into the same number of daughter-colonies of cells, all
resembling one another, which swarm out of the mother-colony
and unite permanently in twos by way of conjugation. In
another flagellate Infusorian, Eudorina elegans, which also
forms colonies, at the time of conjugation two kinds of daughter-
colonies are produced, distinguishable as male and female.
rightly remarks, quite hypothetical. Cf. also 0. Hertwig, pp. 304, &c., where
he discusses the original forms of sexual generation and the first appearance
of differences of sex.
1 In Noctiluca fertilisation follows conjugation after a long or short interval,
and multiplication takes place by a budding process and the formation of
swarm spores. Cf. 0. Hertwig, Allgemeine Biologic, p. 304.
2 The family of Volvocineae, to which belong the species mentioned here,
Pandorina, Eudorina, and Volvox, enjoys the honour of being claimed both
by zoologists and by botanists. The former class it among Flagellata, the
latter among the Green Algae. Cf. R. Hertwig, Lehrbuch der Zoologie, 1905,
p. 171 (Eng. trans, pp. ^201, 202); Strasburger, Lehrbuch der Botanik, 1904,
p. 283 (Eng. trans. 1908, p. 355).
CONJUGATION OF PKOTOZOA 133
The female colonies have sixteen fairly large daughter-cells
of the ordinary shape, and the male thirty-two much smaller
cells resembling spermatozoa and called zoosperms, whilst the
female daughter- cells are called oosperms. The zoosperms
swarm out and penetrate the female daughter-colonies, fusing
in conjugation with their oosperms.
A still higher degree of differentiation in the cells and in the
processes of conjugation is shown by the well-known Volvox
globator, which is also one of the Infusorians forming colonies.
In one of these colonies there are three kinds of cells, viz.
somatic or body- cells, which remain unchanged, and sexual
cells of two distinct shapes, which are formed only at the time
of conjugation. Some of them then become large and round,
and correspond to egg-cells, whilst others change into thread-
like zoosperms, which develop in clusters, then swarm out and
fertilise the oosperms. As real somatic cells are developed in
the Volvox colonies, and serve to unite the whole colony, and
perform the functions of nourishment and growth for it as a
whole, we are justified in regarding Volvox as a single animal
or plant consisting of body-cells and of two kinds of germ-cells.1
This is the link connecting the unicellular animals (Protozoa),
and the phenomena of their conjugation, with the multicellular
animals (Metazoa) and the processes of their fertilisation.
In other Protozoa, especially in the malaria parasites
belonging to the Haemosporidae, the development of which
has been studied chiefly by Grassi,3 and in the allied order
Coccididae, examined at an earlier date by Schaudinn,3 there
are two periods of reproduction, recurring alternately. The
one is sexless, but in the other there are present individuals
differentiated in sex, the so-called macrogametes and micro-
gametes, which unite in conjugation.4
1 Cf. also M. Hartmann, ' Die Fortpflanzungsweise der Organismen,
Neubenennung und Einteilung derselben, erlautert an Protozoen, Volvocineen
und Dicyemidcn ' (Biolog. Zentralblatt, 1904, No. 1, pp. 18-32 ; No. 2, pp. 33-61),
p. 38.
2 Cf. Grassi's address at the Fifth International Zoological Congress, ' Da s
Malariaproblem vom Zoolog. Standpunkt ' (Verhandl. des Kongresses, 1902,
pp. 99-114).
3 ' tiber den Generationswecb.se! der Coccidien und die neuere Malaria-
forschung ' (Sitzungsberichte der Gesellsch, naturforsch. Freunde, Berlin, 1899,
No. 7, pp. 159-78) ; ' Der Generationswechsel der Koccidien und Hamo-
sporidien. Zusammenfassende Ubersicht ' (Zoolog. Zentralblatt, V, 1899, No.
22, pp. 765-783).
4 Cf. M. Hartmann, as above.
134 MODERN BIOLOGY
In the Proceedings of the German Zoological Society for
1905 (Verhandl. der Deutsclien Zoolog. Gesellschaft, pp. 16-35
with Plate I) Fritz Schaudinn has given an excellent summary
of recent investigations on fertilisation among Protozoa. It
appears from this work that ' all forms of coitus known to
occur among other living organisms, both animals and plants,
take place also among Protozoa.' A tabular survey of these
various forms of coitus is given on pp. 20 and 21, for which
Schaudinn is indebted to Stempell.1
I cannot do more than outline briefly the processes of con-
jugation in the lower organisms. They show an extraordinary
variety of forms, and are in many respects instructive for us
when we study the problem of fertilisation. They teach us
that the difference in the germ-cells of higher animals and
plants is designed to render possible the union of two cells
belonging to different individuals, in order to effect the re-
organisation of the vital process of the species. The greater
the difference in form between the two cells, the more perfect
is their physiological division of labour ; inasmuch as the egg-
cell stores up nourishment for the development of the embryo,
and the sperm-cell acquires the greatest possible agility, in
order to be able to enter the egg-cell and stimulate it to
development ; and the more perfectly these ends are to be
attained, the higher is the degree of differentiation in the
problem of fertilisation.
The feature common to all phenomena of fertilisation is
the union of the nuclei of the two cells, whether the latter
resemble one another or not. We cannot call the part taken
by the centrosomes essential in the conjugation of lower
animals, for in most of them, e.g. in Ciliata, the centrosomes
seem to be absent or only temporary. Genuine centro-
somes have certainly been observed in Noctiluca, one of
the Cystoflagellata, and also in Actinosphaerium, one of the
Ehizopods.3
We may perhaps conclude that among higher animals also
the centrosome of the spermatozoon, as an ' organ of division,'
is only an instrument for effecting the nuclear union of the two
1 Vegetatives Leben und Geschlechlsakt. (Reprinted from articles contri-
buted by the Naturwissenschaftl. Verein in Grief swald, XXXVI, 1904.)
2 Cf. Wilson, The Cell, pp. 227, 228 ; R. Hertwig, Lehrbuch der Zoologie,
1905, p. 160 (Eng. trans, p. 190).
NATUKAL PAKTHENOGENESIS 135
germ-cells, and that therefore the union of the male and female
pronuclei is the essential point in fertilisation, and through
the chromosomes of these pronuclei the properties of both
parents are transmitted to their offspring.
6. NATURAL PARTHENOGENESIS
In considering the phenomena of fertilisation and con-
jugation (§§ 3-5) we have found each process to culminate
invariably in the union of the nuclei of two cells. We have
now to refer to those cases in which there is no union of nuclei,
and yet at least the beginning of embryonic development
occurs in the egg or in the ovary. A study of these cases will
help us to arrive at a general understanding of the problem of
fertilisation and heredity.
In the first place we must deal with natural parthenogenesis,1
which occurs in many animals and plants, and consists of the
development of the egg under natural conditions without
fertilisation by a sperm-cell. We are here concerned chiefly
with animal eggs, and we find parthenogenetio deTelopment
occurring especially in Kotatoria among worms, in Phyllopoda
and Ostracoda among Crustacea, and in many butterflies,
(parthenogenesis among Psychidae was discovered by Karl
von Siebold in 1848), in planjrlice and their relations, in
the praying-crickets, gall-flies, saw-flies, wasps, bees^and
antgj. In considering the morphological processes during the
maturation and development of the eggs of these creatures,3
we have to distinguish two cases, viz. that in which partheno-
genesis takes place regularly in definite generations, and is-
obligatory ; and that in which it occurs only incidentally, and
is facultative^ It is true that in the first case parthenogenetic
1 Under this heading we may include paedogenesis, in which parthenogenetic
reproduction is accomplished by animals still in the larval stage of growth,
for instance in Aphididae and in certain Diptera (Miastor and Chironomus).
The remarkable phenomena of polyembryony is connected with paedogenesis ;
in the above-mentioned Diptera, in one larva numerous small larvae develop,
and in the same way in some parasitic wasps (in Encyrtus and Polygnotus
according to Marechal, and in Litomastix according to Silvestri) a number of
embryos develop in one egg (see p. 129). Polyembryony may therefore be
described as a form of parthenogenesis in the egg ; especially when it occurs
in unfertilised eggs, as it does in Litomastix.
2 Cf. Korschelt and Heider, Lehrbuch der vergl. Entwicklungsgesch., pp.
013-622.
136 MODERN BIOLOGY
development is generally, at least in animals, not the exclusive
mode of reproduction, as, at definite intervals in the series of
parthenogenetic generations, they are replaced by sexual
generation (Heterogony). The tendency to parthenogenesis
is, however, stronger than when it is merely facultative.
A study of the maturation of the eggs of animals with
obligatory parthenogenesis shows that as a rule only onejpolar
body is formed,1 but that two are present in those generations
of the same species in which the eggs require fertilisation by
means of spermatozoa. In these generations the normal
number of chromosomes in the cleavage-spindle of the egg has
subsequently to be restored by means of the male pronucleus,
therefore the number is first halved by a reduction within the
egg, and made up again in the course of fertilisation.2
We can, therefore, understand why no reduction takes place,
and why consequently no second polar body is formed, in
eggs that develop parthenogenetically without fertilisation.
That this is the case has been proved from the examination of
parthenogenetic eggs of various classes of animals by Bloch-
mann, Weismann, Ishikawa, Erlanger, Lauterborn, Lenssen,
and Woltereck. Their observations, and especially those
made by Woltereck on the eggs of a Crustacean (Cypris),
render it probable that no reduction in the number of chromo-
somes takes place during the maturation of these eggs, but
that the original number (twelve in Cypris) remains unaltered
until the cleavage-spindle is formed, which constitutes the
first stage in embryonic development.
According to 0. Hertwig, A. Brauer, Viguier, &c., there
are other cases in which a second polar body is formed also in
eggs that develop parthenogenetically, but its formation is
incomplete, as the second polar body remains within the egg
and is eventually reunited with the nucleus. Boveri thought
that the second polar body might replace the spermatozoon,
and that in this case parthenogenesis was the result of self-
fertilisation on the part of the egg. He assumed that the
polar body served, instead of the sperm-nucleus, to restore the
normal number of chromosomes for the first cleavage-spindle
1 This has been confirmed recently by J. P. Stschelkanovzew's examination
of plant-lice. Cf. his article ' Uber die Eireifung bei viviparen Aphiden '
(Biolog. Zentralblatt, 1904, No. 3, pp. 104-112).
2 Cf. pp. 110 and 120.
NATUBAL PAKTHENOGENESIS 137
of the egg. According to Brauer there are two types of
development in the parthenogenetic eggs of Artemia. In
one type the second polar body is formed, but united again
with the egg-nucleus ; in the other type it is not formed at all.
Brauer states that in the first type the number of chromosomes
in the cleavage-spindle of the egg is 168 (the normal number
for this species) ; in the second type it is only 84 (half the
normal number), but, as no division takes place, the chromo-
somes have a double value.
The maturation of the egg of the parasitic Litomastix
truncatellus, as observed by Silvestri in 1905, is remarkably
interesting (see p. 129, note 2). The process is the same in
the parthenogenetic as in the fertilised egg. In both cases
two polar bodies (globuli polari) are formed, and remain in the
front part of the egg. The first polar body divides, but its
two halves unite with one another and with the second polar
body to form a nucleus, which Silvestri calls from its origin
a polar nucleus.
In many insects however, especially in such as have only
facultative parthenogenesis, e.g. in Liparis, Bombyx and
Leucoma among butterflies, and in the honey-bees and many
ants (Lasius) among Hymenoptera, the maturation- divisions
of the parthenogenetic egg result in the complete formation
and separation of two polar bodies. At Weismann's suggestion,
Dr. Petrunkewitsch * made a very careful examination of
the unfertilised eggs of the bee, from which drones are hatched,
and showed this quite conclusively. We can, perhaps, account
for the formation of two polar bodies by assuming that, in
these insects, fertilisation is the normal condition ; where it
does not take place, the egg makes the same preparations for
it as when it does. But in many gall-flies (Rhodites) partheno-
genesis is obligatory, and yet two fully developed polar bodies
are formed, neither of which reunites with the egg. It is a
remarkable fact that when two such polar bodies have been
cast out of the egg, and when the accompanying karyokineses
have reduced the number of chromosomes in the egg by a half,
the normal number nevertheless recurs in the cleavage-spindle.
1 * Die Richtungskorper und ihr Scbicksal im befruchteten und unbefruch-
teten Bienenei ' (Zoolog. Jahrbiicher, Abteilung fur Anatomie u. Ontogenie,
XIV, 1901).
138 MODEKN BIOLOGY
Petrunkewitsch observed this phenomenon in the eggs of the
bee, but was unable to account for it.
Morphological processes closely resembling parthenogenesis
in the animal kingdom occur in the parthenogenetical develop-
ment _of many plants. In 1900 Juel observed1 that in Anten-
j naria alpina the egg developing parthenogenetically in the
/ embryo-sac shows no reduction in the number of chromosomes ;
and in 1901 the same thing was observed by Murbeck3 in
the varieties of Alchimilla that develop parthenogenetically.
\ In 1905 E. Strasburger devoted much attention to the study
of the propagation of the Eualchimillae, and came to the
conclusion that in the seeds of these plants the development
of the mother-cell of the embryo-sac and of the embryo takes
V place without fertilisation. In this case there is no reduction
\ in the original number of chromosomes, which remains constant
as in the somatic cells of the plant. Strasburger prefers to
call this process apogamyj or sexless propagation, rather
than parthenogenesis, or unisexual propagation, because it
takes place on vegetative and not sexual lines. Winkler, on
the other hand, retains the name ' parthenogenesis,' but
calls it in this case somatic, as opposed to the true generative
parthenogenesis.3
In one of the Algae (Ectocarpus siliculosus) an extraordinary
phenomenon has been observed. Not only the female germ-
cell can develop parthenogenetically under certain circum-
stances, but the male cell may also do so ;4 in this case, however,
the difference in size between the two is not great, and the
male plant, corresponding with the' smaller size of the zoo-
sperm, tends to be poorly developed. This is the only case,
occurring under natural conditions, of male parthenogenesis
or arrhenogenesis.
There are many obscure points in natural parthenogenesis,
as we have shown. Only one fact can be stated with certainty,
1 ' Vergleichende Untersuchungen iiber typische und parthenogenetische
Fortpflanzung bei der Gattung Antennaria ' (Svenska Vetenskaps Akad. Handl,
XXXIII, 1900, n. 5).
2 * Parthenogenetische Embryobildung in der Gattung Alchimilla ' (Lunds
Univers. Arsskri/t, XXXVI, 1901, n. 2). '
3 Cf. Strasburger, ' Die Apogamie der Eualchimillen und allgemeine
Gesichtspunkte, die sich daraus ergeben ' (Jahrbiicher fur wissenschaftL
Botanik, LXI, 1905, pp. 88-164). Cf. also the article in the Naturwissenschaft-
liche Rundschau, XX, 1905, No. 27, pp. 342-344.
4 Weismann, Lectures on the Evolution Theory, I, 334.
AKTIFICIAL PAKTHENOGENESIS 139
viz. that, in a good many kinds of animals and plants, the
egg-nucleus alone is able to begin the embryonic development
of the egg. Therefore the union of the nuclei of two cells,
the male and female germ-cells, is not absolutely and universally
essential to the beginning of embryonic development, even in
those organisms which possess both kinds of germ-cells. If
nevertheless, in normal fertilisation, the union of the nuclei
of the two germ-cells is regularly the culminating point of the
whole process, its object is not merely to stimulate the ovum
to embryonic development, but, over and above this, its object
is chiefly to secure the benefits of amphimixis, i.e. the trans-
mission of the combined properties of both parents to their
offspring, and this is brought about by the union of the paternal
and maternal nuclear elements in the cleavage-spindle of the
fertilised ovum.. We must not, however, undervalue the first
object in normal fertilisation. It cannot be denied that a
renewal of the capability of development of the species, a
* reorganisation of the living substance,' is connected with the
union of the germ-cells, and therefore it is still very doubtful
whether an unlimited propagation by parthenogenesis would
be possible, at least in the animal kingdom.1
7. AKTIFICIAL PARTHENOGENESIS
Let us now turn to experiments in artificial parthenogenesis.2
Tichomirow discovered in 1886 3 that in the eggs_of the_silk-
moth, which otherwise require fertilisation, parthenogenesis
may be produced by rubbing them between cloths. The
same result was obtained by Tichomirow both in 1886 and in
1902 by dipping the eggs into concentratedsulphuric and
1 In one Crustacean (Cypris reptans) Weismann states that he observed
uninterrupted parthenogenesis (Zoolog. Anzeiger, XXVIII, 1904, p. 39). It
seems to be possible also in some grasshoppers which are all females (de Sinety,
Recherches sur les phasmes, 1901, pp. 13, &c.). H. Schmitz has made the same
observation in Dixippus morosus, a tropical praying- cricket (' Dixippus
morosus,' in Natur und Offenbarung, 1906, Part 7, pp. 385-407, 402, &c.).
2 A summary of these experiments is given by Korschelt and Heider,
Lehrbuch der vergl. Entwicklungsgesch., pp. 623, &c., 663 &c. ; by Boveri, Das
Problem der Befruchtung, pp. 39, &c. ; by Y. Delage, Les theories de la fcconda-
tion, pp. 135, &c. ; by Kathariner, Das Problem der Befruchtung, pp. 518, &c. ;
by 0. Hertwig, Allgemeine Biologie, pp. 326, &c.
3 ' Die kiinstliehe Parthenogenese bei Insekten ' (Archiv f. Anatomie u.
Physiologic, Supplement, 1886).
140 MODEKN BIOLOGY
muriatic acid. In 1887 0. and K. Hertwig l found that un-
fertilised eggs of sea-urchins could develop under the influence
of external stimulus, and E. Hertwig continued these experi-
ments in 1888 and 1896, and in a work 2 published in the latter
year he describes the processes of division in the egg-nucleus
which result from placing the unfertilised egg of a sea-urchin
in a weak solution of strychnine. Many experiments in
artificial parthenogenesis have been made in the last few years
by American naturalists, Th. Morgan, Jacques Loeb, E. B.
Wilson, and A. B. Mathews, and also by scientists of other
nationalities, such as Y. Delage, Giard, Bataillon, Henneguy,
Herbst, Winkler, Prowazek, Kostanecki, Boveri, WasiliefT.
Schiicking, Petrunkewitsch, &c.3
Unfertilised eggs of very various animals (Echinoderms,
Medusae, Molluscs, Annelids, insects and fishes) were chosen
and exposed to chemical, physical, and mechanical stimuli of
many different kinds. Solutions of various poisons, narcotics
and salts, such as strychnine, nicotine, hyoscyamine, ether,
alcohol, chloroform, calcium chloride, magnesium chloride,
diphtheria serum, a solution of cane sugar, urea, and sperm
extract — all proved efficacious in setting up the processes of
development ; and similar results were obtained by concen-
trating the sea-water containing the eggs, by dipping them in
warm sea-water and by applying galvanic currents and
mechanical vibration. Jacques Loeb's experiments were the
most successful. He was able to cause the unfertilised eggs
of all kinds of Echinoderms and Annelids to form larvae, and
by subjecting those of sea-urchins to the action of chloride of
magnesium for two or three hours he made them develop as
1 ' Uber den Befruchtungs- und Teilungsvorgang des tierischen Eis unter
dem Einflusse ausserer Agentien ' (Jenaische Zeitschr. fur Naturwissenschaft,
XX)
2 Uber die Entwicklung des unbefruchteten Seeigeleis, Festschrift fur C.
Gegenbaur, Leipzig, 1896.
3 Korschelt and Heider give a list of books dealing with the subject, pp. 733,
&c. They do not, however, mention those of the last four authors named
above : Boveri, ' Zellenstudien,' 1902, Part 4, p. 9 ; Wasilieff, ' Uber kunstliche
Parthenogenesis des Seeigeleis ' (Biolog. Zentralblatt, XXII, 1902, No. 24,
pp. 758-772) ; A. Schiicking, ' Zur Physiologic der Befruchtung, Parthenogenese
und Entwicklung ' (Archiv fur die ges. Physiologie, XCVII, 1903) ; A.
Petrunkewitsch, ' Kunstliche Parthenogenese ' (Zoolog. Jahrbiicher, Supplem.
VII, 1904, ' Festschrift flir Weismann,' pp. 77-138). Cf. also a review of the
last-mentioned article in the Naturwissenschaftliche Rundschau, 1904, No. 35,
pp. 444, &c.
ABTIFICIAL PARTHENOGENESIS 141
far as the blastula stage, and finally even as far as
that of the Pluteus larva. These larvae remained alive
for as long as ten days, but were unable to form any
calcareous skeleton, although they developed this power when
carbonate of calcium was added to the sea-water. Loeb
succeeded also in inducing the eggs of an Annelid (diaeto-
pterus) actually to reach the stage of forming the trocho-
phore larva.1 These careful and ingenious experiments seem
to have resulted in the discovery of a magic wand, capable
of awakening the life dormant in the unfertilised animal
ovum ; and apparently they afford a brilliant confirmation of
Aristotle's opinion, for he believed the ovum to contain the
essentials of each animal species, and the spermatozoon merely
to have the effect of stimulating the ovum to develop. Before
we assent to these conclusions, we must examine the results
of these experiments somewhat more closely.
The forms resulting from artificially produced partheno-
genesis differ in many respects from the normal, as Kathariner
already partially pointed out in ' Natur und Offenbarung,'
1903, p. 518. Their cleavage-globules have less power of
resistance ; they show a tendency to fall to pieces, and dwarf
larvae develop from the fragments, or else several cleavage-
globules unite and give rise to gigantic and monstrous embryos.
In the sea-urchin larvae produced parthenogenetically, irregu-
larities in the formation of the skeleton are apt to occur,
and all these artificially developed forms seem to lack some
directive power, which is supplied by normal fertilisation
and results in development on definite lines. The Pluteus
and trochophore larvae, produced by Loeb's experiments, are
the highest achievements of artificial parthenogenesis, but it
is doubtful whether they were really capable of continued
existence and of developing from the stage of larvae to that
of adults, for hitherto no one has succeeded in breeding even
the natural larvae of these species in a laboratory. In any
1 Loeb, ' On the nature of the process of fertilisation and the artificial
production of normal larvae (Plutei) from the unfertilised eggs of the sea-
urchin ' (American Journal of Physiology, III, 1899) ; ' On the artificial pro-
duction of normal larvae from the unfertilised eggs of the sea-urchin ' (1900) ;
' Further experiments on artificial parthenogenesis ' (IV, 1900) ; ' Experiments
on artificial parthenogenesis in Annelids (Chaetopterus) and the nature of the
process of fertilisation ' (IV, 1901).
142 MODEEN BIOLOGY
case, although in a few successful instances larvae were actually
formed, there were many less successful, or even quite un-
successful, attempts at artificial parthenogenesis, in which the
cleavage process, artificially induced, ceased even earlier.
An attempt to account for these variations has been made
by Boveri (' Das Problem der Befruchtung,' pp. 39, &c.) in his
criticism of Morgan and Wilson's experiments. He points out
that, when an ovum is fertilised, only one radiation sphere is
formed at the head of the spermatozoon that has entered.
The division of this radiation sphere gives rise to the two
astrospheres which are the poles of the first nuclear spindle of
the ovum. (Cf. p. 122 and Plate I, figs. 1-7.) According
to the observations of the two American writers, however,
artificial parthenogenesis of the same eggs, under the influence
of Loeb's reagents, results in the formation of a fluctuating,
but often considerable, number of radiation-spheres, each of
which has a newly formed centrosome as its centre. Boveri
believes that regular cleavage of the ovum can occur only in
the exceptional case that only two really active radiation-
spheres develop and take up their positions at opposite poles
of the egg-nucleus ; under all other circumstances the numer-
ous division-centres, having no orderly arrangement, act as
they do in pathological polyspermy, and give rise to an irregular
mass of cells, which speedily dies. Therefore Boveri still
regards the introduction of the spermatozoon into the ovum
as supplying the directive quality, which, in normal fertilisa-
tion, secures the formation of a regular cleavage-spindle with
two poles. It is comparatively of less importance whether
the spermatozoon actually brings its own centrosome with
it into the ovum, or whether, through the chemical and
physical action of the sperm-nucleus, the egg-protoplasm
becomes capable of forming a new centrosome for itself,
which then takes up a position in front of the sperm-nucleus,
and by dividing forms the poles of the cleavage-spindle. The
attempts at artificial parthenogenesis seem to me to support
the theory of the new formation of centrosomes in the ovum ;
and these experiments have in some degree caused me to
modify the account that I previously gave (see p. 125) of the
significance of the normal process of fertilisation, in giving
which I was guided by Boveri's diagrams. (Plate I, figs. 1-7.)
CENTEOSOMES 143
Another remark must be made on the subject. Morgan,1
and still more emphatically Wilson,3 declare that they have
observed the new formation of centrosomes as centres of the
radiation spheres in sea-urchins' eggs parthenogenetically
developed by the application of chloride of magnesium, and
Wilson describes the new formation of centrosomes in non-
nucleated fragments of an egg.3 Wasilieff, on the other hand,4
in his corresponding experiments with strychnine, nicotine
and hyoscyamine, found that the first divisions took place
without the formation of centrosomes, which, if they appeared
at all, did so only in the later stages of cleavage, and were then
formed of the nuclear substance of the cells. The occurrence
of true centrosomes in non-nucleated fragments of an egg is
questioned also by Petrunkewitsch.5
Should the observations of Wasilieff and Petrunkewitsch
find confirmation, we shall have greater reason for regarding
the centrosomes, not as a permanent formation, but as only
a temporary biomechanical means of assisting the process of
cell-division. (Cf . Chapter V, pp. 98, &c.) If this be so, we must
consider the appearance of a centrosome beside the sperm-
nucleus in normal fertilisation of the animal ovum, not as the
cause of cell- division, but as a consequence of the beginning of the
process. We shall then have to agree with Oskar Hertwig's
older theory of nuclear fertilisation, and say, that in normal
fertilisation also, the entrance of the sperm-nucleus into the
ovum and its union with the female pronucleus constitute the
real elements of fertilisation.
The question of chromatin-reduction is another point
connected with artificial parthenogenesis on which opinions
are divided. The eggs used in the experiments, to which I
have referred, were such as had undergone their maturation-
divisions, and so we must assume that the nucleus of each
contained only half the number of chromosomes peculiar to the
1 ' The production of artificial astrospheres ' (Archiv fur Entwicklungs-
mechanik, III, 1896).
2 ' Experimental studies in cytology,' I. ' Artificial parthenogenesis in
sea-urchin eggs ' (Ibid. XII, 1901).
3 ' Cytasteren und Centrosomen bei kiinstlicher Parthenogenese ' (Zoolog.
Anzieger, XXVI, 1904, pp. 8-12).
4 ' tiber kiinstliche Parthenogenesis des Seeigeleis ' (Biolog. Zentralblatt,
1902, pp. 758-772).
5 ' Kiinstlicho Parthenogenese ' (Zoolog. Jahrbiicher, Supplem., VII, 1904,
77-138).
144 MODEEN BIOLOGY
species. Wilson states expressly that he found eighteen and
not thirty-six chromosomes in the cleavage-cells of the sea-
urchins' eggs undergoing pa-rthenogenetic development. Y.
Delage, however says that in his experiments on the same
eggs he found the normal number of chromosomes to be
restored. Boveri argues1 that eighteen, which Delage appar-
ently took to be the normal number, is really the reduced
number for that species, for his own observations and those
of E. Hertwig both show thirty-six to be the normal. We
must probably assume that, when eggs develop by artificial
parthenogenesis, half the normal number of chromosomes
suffices for the cleavage-nucleus of the developing ovum.
Petrunkewitsch has gone so far as to state (1904) one essential
difference between artificial and natural parthenogenesis to be
that, in the former, the reduced number of chromosomes
invariably remains.
We may now turn to the more general conclusions formed
by various students, as resulting from the experiments in
artificial parthenogenesis.
Loeb thinks he is justified by his experiments (see p. 140)
in concluding that the ova of many, and perhaps of all, animals
have a certain tendency to develop parthenogeneticaliy, but
as a rule this development is so slow that the ovum perishes
before it attains to any advanced stage of cleavage. Artificial
stimuli, such as salt solutions, &c.; by hastening the develop-
ment, enable the ovum to attain its end parthenogenetically.
Korschelt and Heider, on the contrary,2 and E, Hertwig3
incline to the far more moderate opinion that the chemical
and physical stimuli are able to set up in the mature, but still
unfertilised, ovum that reciprocal action of the parts (and
especially of the cytoplasm and nucleus) which is indispens-
able to embryonic development, and which under normal con-
ditions results only from fertilisation. Boveri4 thinks that the
1 ' "Dber mehrpolige Mitosen als Mittel zur Analyse des Zellkerns ' ( Verhandl.
der physikal.-mediz. Gesellsch., Wiirzburg, XXXV, 1902).
2 Lehrbuch der vergl. Entwicklungsgesch., p. 624 ; cf. also ibid. pp. 65-67.
3 ' tJber Korrelation von Zell- und Kerngrosse und ihre Bedeutung fiir
die geschlechtliche Differenzierung und die Teilung der Zelle ' (Biolog. Zentral-
blatt, 1903, Nos. 2 and 3) ; also * Uber das Wechselverhaltnis von Kern
und Protoplasma,' Munich, 1903. (Reprinted from the Miinchener Medizin,
Wochenschrift, I.)
4 Das Problem der Befruchtung, pp. 22-23, 39, &c.
THEOKIES REGARDING FERTILISATION 145
phenomena observed in artificial parthenogenesis afford a con-
firmation of his theory of fertilisation, according to which the
mature ovum resembles a complete piece of mechanism, still
at rest, and needing only to be wound up, in order to begin to
work. The key to it is, in normal fertilisation, the centrosome
of the spermatozoon ; but in artificial parthenogenesis it
consists of some chemical or physical agents ; which affect the
egg-plasm in a way similar to the action of the centrosome
under ordinary circumstances. As early as 1886 Tichomirow
put forward the theory that the egg-cell responded to all
exterior action — no matter of what kind — invariably in the
same way, peculiar to itself, viz. by development ; just as
the cells of the optic nerves react invariably through their
susceptibility to light, and the cells of the muscular fibres
contract under external stimulus. This idea was borrowed
from Johannes Miiller's law of specific energies of the senses.
The same view has been recently formulated by Y. Delage in
the following terms : ] ' The mature but still unfertilised
ovum is in a condition of unstable equilibrium ; any stimulus,
destroying the equilibrium, gives rise to development.'
Loeb goes perhaps rather too far when he says that all
animal ova have an original tendency to parthenogenetic
development, for the results of experiments show that artificial
parthenogenesis seldom attains the normal end, and that the
cleavage stages thus produced cease, as a rule, without develop-
ing to a larva. Moreover, at the present time most zoologists
agree in regarding natural parthenogenesis, where it actually
occurs among animals, not as the original mode of develop-
ment, but as a later simplification of the original mode ;
they believe propagation by fertilisation to be the. normal
condition.
We must therefore not overestimate the capacity of many
eggs to develop without fertilisation under artificial stimulus ;
but, on the other hand, we must not underestimate it, for, taken
in conjunction with natural parthenogenesis, it proves plainly
enough that under certain circumstances one nucleus alone,
viz. the egg-nucleus, suffices to begin embryonic development.
The chief object, then, of the union of two different nuclei in
normal fertilisation is not merely to stimulate the ovum
1 Les theories de la fecondation, p. 138.
146 MODEEN BIOLOGY
to develop, but rather to secure the benefits of amphimixis, i.e.
of transmitting to the offspring the properties of both parents,
and this is effected by the union, in the cleavage-spindle of
the ovum, of the nuclear elements of the male and female
pronuclei. I shall recur to this subject at the end of the
present chapter.
The other object of fertilisation, viz. to stimulate the
ovum to develop, can be attained by very various means
without fertilisation, as the experiments in artificial par-
thenogenesis prove.1
As Delage puts it the mature egg really gives us the im-
pression of being in a state of unstable equilibrium ; anything
that disturbs that equilibrium suffices to cause the egg to
develop.
Closely akin to this idea is the further suggestion that,
in normal fertilisation also, there may be certain chemico-
physical processes which result in the development of the
egg. Thus we arrive at the physical and chemical theories
of fertilisation, which have been propounded in the last few
years. They are still hardly ripe for discussion, and consist
chiefly of rather vague speculations, so we may limit ourselves
to what is absolutely necessary in dealing with them.
The question to be answered is : 'In normal fertilisation,
what does the spermatozoon bring into the ovum to render
it capable of development ? ' The answer given by Boveri's
morphological theory is : 'In its centrosome the spermatozoon
imports a new division-centre into the ovum.' The physical
and chemical theories, however, reply : ' The spermatozoon
produces in the ovum certain physical and chemical changes
which result in the process of division.'
The two classes of theories are not necessarily antagonistic,
but are complementary. Carnoy and Biitschli had already
suggested that the centrosomes stimulate the cell to divide,
by exerting some chemical influence on the protoplasm,
and Boveri himself expressed an idea, which Wilson subse-
quently elaborated, that possibly some chemical substance,
1 I must remind the reader here, as I did on p. 141, that this object is only
imperfectly attained by artificial parthenogenesis. We must therefore
assume that a particular kind of ' reorganisation of the vital substance '
is connected with natural fertilisation, and especially with the union of the
nuclei.
THEOEIES EEGAEDING FEBTILISATION 147
stimulating the ovum to develop, is brought into it by the
spermatozoon.1
The morphological theory only shows itself really anta-
gonistic to the chemico-physical theory, when there is a choice
between one or other of them, as being exclusively valid ; J.
Loeb seems inclined to adopt the chemico-physical theory,
in spite of the obscurity in which it is still involved. There
is a wide divergency of opinions regarding the nature of the
chemical and physical processes which underlie fertilisation.
Loeb, the chief champion of the new theory, originally thought
that electrolysis might account for it, and that new metallic
ions were brought by the spermatozoon into the ovum. Subse-
quently, he came to the conclusion that some alteration in
the osmotic conditions of the ovum was effected by the action
of the spermatozoon. In 1900, Wilson suggested that the
middle-piece of the spermatozoon, which contains its centro-
some, might be the bearer of a specific chemical substance
stimulating the ovum to development, quite apart from the
sperm-nucleus. Finally, Yves_Delage has set up a still simpler
hypothesis of chemical and physical fertilisation ; e he thinks
that the ovum becomes capable of fertilisation in consequence
of the breaking up of the nuclear membrane during the matura-
tion-divisions, and the distribution of the nuclear fluid to the
protoplasm of the ovum. The head of the spermatozoon
penetrating the ovum becomes the male pronucleus, and
grows by taking up water from the egg-plasm, thus depriving
it of some of its fluid. In this dehydration of the ovum by
the sperm-nucleus Delage thinks he has discovered the chemico-
physical cause of the beginning of the dividing process in the
ovum. He does not, however, exclude the specific action of
salts, metallic ions, &c., which may be contained in the sperm-
nucleus.
Loeb considered that his experiments in artificial partheno-
genesis had transferred the problem of fertilisation from the
domain of morphology into that of chemico-physical science.
1 .Cf. Korschelt and Heider, Lehrbuch der vergl. Entwicklungsgesch., pp. 663,
&c., and Wilson, The Cell, pp. 354, &c. The phenomena of natural partheno-
genesis are against these theories, as in that case there is no spermatozoon,
nor any special chemical stimulus, present.
2 On this theory and those akin to it, see Y. Delage, Les theories de la
fecondation, pp. 135, &c.
L 2
148 MODEKN BIOLOGY
Y. Delage seems to share this opinion, and Max Verworn has
long desired to replace the morphological theory of fertilisation
by a physiological one. Quite recently B. Hatschek too has
brought forward a new ' Hypothesis of organic inheritance '
(' Hypothese der organischen Vererbung,' Leipzig, 1905) based
upon a physiological and chemical foundation. I agree with
Boveri l in thinking that this bold speculation is still far from
having a basis of ascertained scientific facts. After showing
what a vast number of distinct morphological problems are
involved in the fertilisation, cleavage, and embryonic develop-
ment of the ovum, with regard to the physical and chemical
factors of which we still know nothing at all, Boveri continues :
' As we have said, a transference of the problem of fertilisation
into the domain of physico-chemical science would involve
the assumption that the process of cell-division has been traced
back to physical and chemical factors. How far we really
are from having accomplished this is known to everyone who
has studied the question ; and it is scarcely possible at the
present time to speculate as to how deeply we may eventually
penetrate into the mystery.'
The problem of fertilisation and heredity is, at any rate, no
merely morphological problem ; on the contrary, its physio-
logical aspect is the chief point, as enabling us to understand
the morphological processes, but the morphological and
physiological aspects must be taken in conjunction to support
and complete one another.
My opinion regarding the importance of artificial partheno-
genesis as bearing upon the problem of fertilisation may be
expressed thus : These ingenious experiments have proved
that the problem of fertilisation must not be studied, as has
been done hitherto, exclusively by morphological methods,
but also by completely new methods belonging to physico-
chemical science. Only in this way shall we arrive at a satis-
factory insight into the true nature of the fertilisation and
cleavage of the ovum, and the embryonic development that
follows these processes. For the present we have no certain
information, but only bold speculations, as to the physico-
chemical factors engaged in these processes, nor do we know
how they co-operate mechanically and teleologically to accom-
1 Das Problem der Befruchtuny, p. 47.
MEKOGONY 149
plish them. The naturalists who fancy that they have at
last succeeded in giving a purely physico-chemical explanation
to life itself are doomed to disappointment.
8. THE FERTILISATION OF NON-NUCLEATED EGG-FRAGMENTS
(MEROGONY)
There still remains one class of phenomena which we must
consider shortly, because it throws some light on the problem
of fertilisation, namely, artificial fertilisation of non-nucleated
fragments of ovum, called by Y. Delage merogony.1 The
first experiments, now become classical, in this subject were
begun in 1887 by 0. and K. Hertwig, and continued by Boveri
in 1889 and 1895. They resulted in the surprising discovery
that non-nucleated fragments of sea-urchins' ova could,
if fertilised, develop to the larval stage. Others have subse-
quently confirmed this discovery by means of experiments on
the eggs of sea-urchins and other animals ; we may mention
particularly Morgan (1895), Ziegler (1896 and 1898), and
Delage (1898, 1899 and 1901). Similar experiments were
made by Eawitz in 1901 on the immature eggs of holothurians,
the nucleus of which is unimportant and in course of time
disappears, so that they may be regarded as non-nucleate.
In 1896-8 H. E. Ziegler made some experiments at artificially
constricting sea-urchins' eggs, and his results are not without
bearing on the question.2
Experiments in merogony have been made with plants
also, and I may draw attention particularly to those undertaken
in 1901 by Hans Winkler on the eggs of a seaweed (Cystosira).^
Let us now examine some of the above-mentioned experiments
more closely.
Oskar and Eichard Hertwig succeeded in proving4 con-
clusively that, if sea-urchins' eggs are broken by shaking
fragments containing no nucleus may be fertilised by the
1 Of. Korschelt and Heider, Lehrbuch der vergl. Entwicklungsgesch , pp.
149-151 and 625-626.
2 A full list of the works to which I have referred will be found in Korschelt
and Heider, pp. 733-750.
3 H. Winkler, ' tJber Merogonie und Befruchtung ' (Jahrbiicher fur wissen-
schaftl. Botanik, XXXVI, pp. 753-775).
4 ' Uber Befruchtungs- und Teilungsvorgange des tierischen Eis ' (Jenaische
Zeitschrift fur Naturwissenschaft, XX, 1887).
150 MODEKN BIOLOGY
entrance of a spermatozoon. In Boveri's experiments, such
non-nucleated fragments of the ovum, after fertilisation with
one spermatozoon of the same species, developed and actually
reached the stage of the Pluteus larva, thus showing such ova
to be capable of normal development. In this way Boveri
obtained dwarf larvae, larger or smaller according to the size
of the fragment of ovum.
The experiments made by Hertwig and Boveri prove that
under certain conditions the sperm-nucleus alone, without
the egg-nucleus, suffices for the fertilisation and development
of the animal ovum, in exactly the same way as, in partheno-
genesis, the egg-nucleus suffices without the sperm-nucleus.
Giard called this phenomenon simply male parthenogenesis, as
in this case the sperm-nucleus receives from the non-nucleate
egg-cell the cytoplasm necessary for its development. The
same idea had been expressed somewhat differently by M.
Verworn in 1891, and in 1901 Kawitz invented the name
epliebogenesis to designate the process.
The embryos of the non-nucleated eggs of sea-urchins only
reached the stage of cleavage into sixteen cells in Morgan's
experiments,1 but he was able to demonstrate that their nuclei
contained only half the normal number of chromosomes
(eleven instead of twenty-two) belonging to that species. It
is easy to see why this is so, for the sperm-nuclei, which fer-
tilised the fragments of egg, contained the reduced number.
This fact therefore agrees with similar phenomena observed
in artificial parthenogenesis (see p. 144), and shows that some-
times half the normal number of chromosomes suffices for the
embryonic development of the egg. Whether these chromo-
somes are paternal or maternal in origin is immaterial for the
purpose of embryonic development, but not for that of heredity,
as Boveri's next experiments show with a degree of probability
almost amounting to certainty.3
He began by crossing two distinct varieties of sea-urchin,
and fertilised ova of Sphaerechinus granularis with spermatozoa
of Echinus microtuberculatus. The Pluteus larvae of these
two species can easily be distinguished — those of Echinus have
1 ' The fertilisation of non-nucleated fragments of Echinoderm eggs '
(Archiv fur Entwicklungsmechanik, II, 1895).
2 ' Ein geschlechtlich erzeugter Organismus ohne miitterliche Eigenschaften '
(Sitzungsberichte der Gesellschaft fur Morph. und Phys., Munich, 1889).
MEKOGONY
151
a much more slender shape and a different formation of the
calcareous skeleton. Boveri succeeded in showing that the
result of crossing these two species was to produce hybrid
larvae (fig. 26) occupying a position midway between the two
larvae of pure breed (figs. 24 and 25) and displaying a mixture
of the peculiarities in shape of both parents.
Boveri next proceeded to fertilise ova of Sphaerechinus,
partially broken by shaking, with spermatozoa of Echinus.
Of the larvae produced by the fragments, some showed the
hybrid type, and Boveri assumed that they developed either
from uninjured ova, or from fragments containing part of the
FIG. 24.
FIG. 25.
FIG. 26.
FIGS. 24-26.— Side view of Pluteus larvae: FIG. 24 of Echinus, FIG. 25 of
Sphaerechinus, FIG. 26 of the hybrid of Sphaerechinus <j? and
Echinus 3.
From Korschelt and Heider, according to Boveri's diagram.
egg-nucleus, into which a spermatozoon of the other species
had found its way. Other larvae were particularly small, but
displayed the pure Echinus-type (fig. 24). Boveri calls these
dwarf Plutei, and believes them to have developed from non-
nucleated fragments of Sphaerechinus ova, and therefore to
represent altogether the paternal Echinus-type, because the
sperm-nucleus fertilising them belonged to this latter species.
According to Boveri's view, these dwarf Plutei are organisms
without any maternal characteristics, and, if this view is the
true one, we have here a proof that the cell-nucleus does
not merely determine the shape of the embryo, but is the real
bearer of heredity, for only the cell-nucleus on the father's
side, and not the egg-plasm on the mother's side, stamped
152 MODEEN BIOLOGY
upon the embryo its specific characteristics as a pure Echinus
larva.
Boveri's explanation is rendered more probable by the fact
that the dwarf Plutei of the Echinus type possessed an un-
mistakably smaller nucleus than larvae of the same size of the
hybrid type. This difference in the size of the nucleus is quite
intelligible if we may assume that in the former case the cell-
nucleus was formed from only one pronucleus, and so con-
tained only half the amount of chromatin, whereas in the
second case the nucleus was produced by the union of two
pronuclei.
Boveri assumed, therefore, that the dwarf larvae of pure
Echinus-type, produced in the course of his experiments at
cross-breeding, really developed from non-nucleated fragments
of ovum, and consequently were organisms devoid of any
maternal characteristics. Morgan, Seeliger, Driesch and Delage
have brought forward a number of objections to this theory,
but Boveri adheres to it even in his most recent works. Yves
Delage himself classes Boveri's experiments among what he
calls experiences decisives, as furnishing evidence of great
weight in the solution of the scientific problem under dis-
cussion. In fact, when we take into consideration, firstly,
that non-nucleated fragments of sea-urchins' eggs can be
fertilised, and, secondly, that Boveri fertilised them with
spermatozoa of another species, we can hardly avoid agreeing
with him in regarding the dwarf larvae, which display only
paternal characteristics', as the products of non-nucleated ova,
deriving from the father's side alone their nucleus, and con-
sequently the substance which bears heredity.
Quite recently E. Godlewski has made experiments l at
cross-breeding between sea-urchins (Echinidae) and sea-lilies
(Crinoidea), by fertilising the eggs of the former with sper-
matozoa of the latter, and the results which he obtained are
exactly the reverse of Boveri's. All the hybrid larvae displayed
purely maternal, and no paternal characteristics, even in cases
where a non-nucleated fragment of Echinus ovum was fertilised
with an Antedon spermatozoon. Godlewski argues from this that
Boveri's whole morphological theory of heredity is untenable,
1 ' Untersuchungen iiber die Bastardierung der Echiniden- und Crinoiden-
familie ' (Archiv jiir EntwicUungsmechanik, XX, 1906, pp. 579, &c.).
MEROGONY 153
and Verworn's physiological theory must be substituted
for it ; and that not the chromosomes, but the egg-plasm,
constitute the vehicle of transmission. Such far-reaching
conclusions need confirmation from other experiments before
they can be accepted, for the bulk of the evidence afforded
by biology seems to show decisively that the chromosomes of
the nucleus are the material bearers of heredity. The physio-
logical fact that the chromosomes of the nucleus and the proto-
plasm of the egg act reciprocally upon one another, is of course
included as a fully recognised condition.
The successful attempts made by Boveri and others to
fertilise non-nucleated fragments of ova show that under
certain circumstances the sperm-nucleus alone suffices for the
development of the egg. But this statement does riot imply
that it is the sperm-nucleus itself which gives rise to the process
of development : it may be the sperm-centrosome which pene-
trates into the egg with the nucleus. An observation made by
Boveri in 1887 on the subject of ' partial fertilisation ' suggests
that this may be the case. He saw a spermatozoon enter a
sea-urchin's egg. Its nucleus remained near the periphery
of the egg, whilst the centrosome alone with its amphiaster
approached the egg-nucleus, and thereupon the first cleavage-
division of the egg-nucleus took place. The sperm-nucleus
united with one of the daughter-nuclei of the egg. Wilson, too,
considers that l this observation affords a beautiful illustration
of Boveri's theory that it is the centrosome of the sperm-nucleus
which supplies the normal stimulus to division on the part of
the ovum.
Further light is thrown upon this interesting question by
the experiments made by H. E. Ziegler in 1896 and 1898 on
sea-urchins' eggs, which he fertilised artificially and then
divided by constricting them with fine threads.3
In every case in which the egg was so divided that the
sperm-nucleus, with its centrosome and centrosphere, was
contained in one-half of the egg, and the egg-nucleus in the
other half, the former half divided in the ordinary manner,
whereas an aster was formed near the egg-nucleus, and all
1 The Cell, p. 190.
2 Cf. H. E. Ziegler, * Experimented Studien iiber die Zellteilung : I. Die
Zerschniirung der Seeigeleier ; II. Furchung ohne Chromosomen ' (Archiv
fur Entwicklungsmechanik, VI, 1898, Part 2, pp. 249-293).
154 MODEEN BIOLOGY
preparations were made for cell-division, which, however, never
actually took place. These experiments seem to show again
that, in normal fertilisation, it is the sperm-centrosome that
renders the egg-nucleus capable of active division. In some
experiments made in 1897 and 1901, Boveri broke up some
sea-urchins' eggs after fertilisation, and found asters, leading
in some cases to cell- divisions, also in fragments containing
only egg-nucleus, and no particle of the sperm-nucleus or its
centrosome. Wilson, Winkler, and others are inclined to
explain this last phenomenon by assuming that, as soon as
the spermatozoon enters the egg, its centrosome sets up a
kind of fermentation l in the whole egg-plasm, so that even the
parts remote from the centrosome are stimulated to division.
This explanation would bring us back to the chemical side of
the problem of fertilisation, and, as was said on p. 148, we
cannot do more at present than advance some vague specula-
tions on the subject.
The experiments in merogony suggest this question : Is
it possible that the sperm-centrosome alone, without the
sperm -nucleus and without the egg-nucleus, has the power
of setting up a regular process of division and so of beginning
embryonic development in the fragments of ovum ?
In 1897 Boveri made an experiment 3 and fertilised some
non-nucleated fragments of Echinus eggs with spermatozoa
of another species (Strongylocentrotus). It happened that the
whole nuclear substance of both nuclei passed into one half
of the egg, and the centrosome alone into the other. The
former half divided in the regular way, but in the other a
series of divisions took place in the centrosomes and attraction
spheres, but no cell-division "occurred. This observation led
Boveri to conclude that, at any rate for sea-urchins, at least
one nucleus is indispensable for cell- division. H. E. Ziegler,
however, believes that he succeeded in 1898 in effecting a
' cleavage without chromosomes.' In an egg of Echinus
microtuberculatus, fertilised with spermatozoa of the same
species, at the first division the entire nuclear substance of both
the sexual nuclei passed into one of the cells formed by division,
1 Cf. Korschelt and Heider, Lehrbuch der vergl. Entwicklungsgesch., pp.
663-665.
2 * Zur Physiologie der Kern- und Zellteilung ' (Sitzungsberichte d. physilc.-
mediz. Gesellsch., WErzburg).
PEOCESS OF FEKTILISATION 155
whilst a centrosome with its centrosphere was left in the other.
The cell containing the nuclei divided with perfect regularity,
but also in the non-nucleated cell a series of cleavages took
place in the cell-body ; they were, however, incomplete and
irregular. It is unfortunate that in this interesting experi-
ment Ziegler did not use nuclear stains, but only treatment
with acetates, to prove that there was really no chromatin
present in the division-cell that apparently contained no
chromosomes. This flaw has left the matter still doubtful.
My own opinion is that, in these instances of merogony also,
the centrosome is a biomechanical instrument for assisting
nuclear division, but is not an independent division-organ of
the cell. It is true that the experiments described above
confirm Boveri's opinion (cf. p. 126), that in the case of most
animal ova the centrosome of the spermatozoon gives the
immediate impulse to cell-division in the normal course of
fertilisation, but it is not absolutely indispensable to the
beginning of the process of embryonic development. This is
proved by the phenomena of natural and artificial partheno-
genesis (see pp. 135 and 139), where no male centrosome can
possibly be present. Moreover, many circumstances to which
I have referred (see p. 143) suggest the idea that centrosomes
are not permanent organs in the cell, but are formed afresh
in the egg-plasm as occasion requires.
9. GENERAL EEVIEW OF THE SUBJECT OF FERTILISATION
AND CONCLUSIONS
(See Plate II)
We have now completed our examination of the relations
in which cell-division stands to the problems of fertilisation
and heredity. The facts to be taken into account are so
numerous and of so many kinds, and the interpretations put
upon them are so varied, that it is naturally no easy task to
draw from them any clear and definite conclusions. We
might almost say that we cannot see the wood because of the
trees in it ! And yet the wood is one whole, composed of the
trees which various naturalists have laboriously planted and
cultivated. And there are some paths through it, though
156 MODEEN BIOLOGY
they are still footways and not carriage drives, for the wood is
still wild, and not a park.
Let us try now to follow these paths by surveying the facts
once more and seeing in what respects they conform to general
laws. We must be on our guard against adopting the methods
of those theorists who simply cast aside and reject all that
does not coincide with their subjective ideas.
Both the male and the female germ-cells prepare for their
union in the process of fertilisation by a double maturation-
division. These preparatory divisions cause a reduction in the
number of chromosomes (if it has not taken place before),
so that the cells contain only half the normal number contained
in the somatic cells of the same species. The act of fertilisa-
tion restores the number to the normal, as the chromosomes
of the male and female pronuclei meet in the cleavage-spindle
of the ovum, and by splitting lengthwise furnish an equal
number of paternal and maternal chromosomes for the daughter-
nuclei of the ovum in process of cleavage.
Normal fertilisation has as its essential feature the union
of two germ-cells, one being male and the other female, and
the union is more especially a union of their nuclei. E. B.
Wilson sums up this result on p. 230 of his excellent work
' The Cell ' (1902) in the following words : ' We thus find the
essential fact of fertilisation and sexual reproduction to be a
union of equivalent nuclei ; and to this all other processes are
tributary.' This is true both of the animal and of the vegetable
kingdom. With reference to the latter Wilson says (p. 216) :
' The essential fact is everywhere a union of two germ-nuclei —
a process agreeing fundamentally with that observed in animals.'
Eichard Hertwig uses similar language in the seventh edition
of his ' Lehrbuch der Zoologie,' 1905, p. 124 (Eng. trans, p. 149) :
' Since not until this point (i.e. the union of the sexual nuclei)
is fertilisation complete, we arrive at the fundamentally
important proposition that the essential feature of fertilisation
consists in the union of egg- and sperm- nuclei.'
Nuclear union can, however, assume various forms. It
may — as in the Echinus-type — lead to the formation of a
resting cleavage-nucleus, in which the chromosomes of the
two pronuclei are already brought into contact, or — as in the
^4scans-type — the two pronuclei may remain apart, so that
PEOCESS OF FEKTILISATION 157
their chromosomes are not grouped in a common division-
figure until the cleavage-spindle is formed. Moreover, the
part played by the centrosomes in the processes of fertilisation
varies. In normal fertilisation of the animal ovum, the male
centrosome acts as an organ of division, inducing the formation
of the cleavage-spindle, but no centrosomes have been observed
in the fertilisation of the higher orders of plants. In many
animal ova (e.g. Myzostoma, according to Wheeler) the place
of the sperm-centrosome as an organ of division seems to be
taken by the oocentrosome. Finally, in physiological super-
fecundation among animals and in double-fertilisation among
angiosperms in the vegetable kingdom, not only one sperm-
nucleus, but two or more, are concerned in the process of
fertilisation, although only one, which unites with the egg-
nucleus, has a distinctly generative function, the duty assigned
to the others being rather of a vegetative character, and con-
sisting of the formation of nourishment for the embryo.
So far we have spoken only of the usual case in which two
nuclei, the male and female pronuclei, carry on the fertilising
process in the ovum. Analogous to this are the phenomena
of conjugation which occur in unicellular organisms. But in
artificial fertilisation of non-nucleated fragments of ovum,
only the sperm-nucleus is concerned, and in animal eggs this
is generally accompanied by a sperm-centrosome.
In parthenogenetic development of the ovum there is no
fertilisation by a spermatozoon, but the process is carried on
by the egg-nucleus alone ; in natural parthenogenesis it is
assisted by the oocentrosome, and in artificial parthenogenesis
by centrosomes newly formed in the egg-plasm by means of
exterior agents. WasiliefT considers that even these centro-
somes may be absent. The centrosome alone, without either
egg- or sperm-nucleus, seems to be able to begin the process of
cell-division, but not to succeed in carrying it through.
Let us now sum up the results of these observations and
experiments.1 It seems safe to infer from them that the nucleus
of the germ-cell is of primary importance in normal fertilisation,
as well as in artificial fertilisation of non-nucleated fragments
of ova, and in parthenogenesis. Opinions are still divided
1 Cf. on this subject Korschelt and Heider, Lehrbuch der vergl. Entwick-
lungsgesch,, pp. 697-706 (' Wesen und Bedeutung der Befruchtung ').
158 MODERN BIOLOGY
as to the centrosomes, whether they originate in the achro-
matic nuclear substance or in the egg-plasm ; they seem
to me to be of secondary importance as merely assisting the
division of nucleus and cell. That the egg-plasm is an essential
factor in the processes of fertilisation and development is
proved beyond question, especially by the phenomena of
artificial parthenogenesis, which gave rise to the modern
chemico-physical theories regarding fertilisation.
What, then, is the answer to the question raised by Aristotle,
and repeated from age to age in the course of the dispute
between ovulists and animalculists : * Is the essence of the
animal and vegetable species contained in the egg-cell or
in the sperm-cell ? ' l
Many facts, and especially the phenomena of natural and
artificial parthenogenesis (see pp. 135, 139, &c.) seem to support
Aristotle's opinion that the material required to form the new
individual is all contained in the egg-cell, and that the sperm-
cell only supplies the stimulus causing this material to develop.3
In a modernised form this opinion is revived in Boveri's
theory of fertilisation, which regards the ovum as a complete
piece of clockwork, lacking only the mainspring, or rather,
lacking only the key to wind up the mainspring. This key
is the sperm-centrosome, that sets in action the dividing
process of the ovum. The same fundamental idea is present in
Delage's chemico-physical theory of fertilisation, according
to which the mature but unfertilised egg-cell is in a state of
unstable equilibrium ; this equilibrium is disturbed by a
reduction in the water of the egg-plasm, caused by the entrance
of the spermatozoon, and the ovum is thus stimulated to
independent development.
Other considerations of no less weight are directly opposed
to the theory that the egg-cell alone contains the essence of the
new individual. The experiments in artificial impregnation of
non-nucleated fragments of ova, and especially the results
obtained by Boveri (see p. 150), show that the sperm-nucleus
alone — just as in parthenogenesis, the egg-nucleus alone — in
conjunction with the egg-plasm, is able to cause the egg to
1 Cf. p. 104. See also 0. Hertwig, Allgemeine Biologie, p. 352.
2 Cf. Aristotle, * De animalium generatione,' cap. 2 (Aristotdis opera omnia,
ed. Didot, III, 320). Aristotle docs not of course speak of the elements of
reproduction as cellular, for he had no knowledge of cells at all.
NOKMAL FEKTILISATION 159
produce a new individual of the species concerned. The
embryonic material for the formation of the new individual
must therefore be contained as completely in the nuclear
substance of the spermatozoon as in that of the ovum. The
nuclei of both germ-cells have then with regard to the develop-
ment of the embryo the same prospective potency, as Driesch
calls it.
Let us now turn to a third series of phenomena,
viz. to the facts of normal fertilisation, which are of great
importance for our purpose (cf. pp. 119, &c.). We have already
seen that the process of fertilisation culminates in the union of
the nuclei of the two germ-cells, and that the originally insigni-
ficant sperm-nucleus finally becomes exactly equivalent to
the egg-nucleus in size and shape and in number of chromo-
somes. The sperm-nucleus supplies for the development
of the new individual exactly the same amount of chromatin
nuclear substance as the egg-nucleus ; the nuclear substance of
the cleavage-spindle of the embryo represents the sum of that
contained in the nuclei of the ovum and spermatozoon ; the
essence of the animal or vegetable species, as propagated by
normal fertilisation, is therefore first contained in the sum of the
chromatin nuclear substance of the male and female pronuclei,
and the essence of normal fertilisation culminates therefore in the
union of the chromosomes of both to form one new cell-nucleus.1
In his 'Allgemeine Biologie' (1906), p. 301, 0. Hertwig states
his conclusions in the following words : ' The nuclear sub-
stances supplied in exactly equal quantities by two distinct
individuals are the especially active materials, the union of
which is the chief object of the act of fertilisation ; they are
the real materials of fertilisation.' 3
We cannot avoid asking further questions : What is the
object of this union of paternal and maternal nuclear elements
in the normal course of fertilisation ? Is it not altogether
superfluous, if what is essential to the species is contained
1 This explains why the number of chromosomes in the somatic cells of
animals and plants that are propagated by sexual reproduction is always even.
Cf. Chapter V, p. 92.
2 A detailed proof that the nucleus is the physical basis of inheritance
is given by Hertwig in the thirteenth chapter of the same work, pp. 354-363.
His proof depends upon four kinds of evidence, which agree on the whole with
those that I have adduced.
160 MODEKN BIOLOGY
completely either in the egg-cell alone, or in the sperm-cell alone ?
What is the use of the vast difference between the ovum and
the spermatozoon in the higher organisms, where the former
is very large and richly provided with nutritive plasm, and
the latter is diminutive and consists of a thread of cytoplasm
by way of tail, a head containing a nucleus, and a middle-piece ?
What is the use of the complicated maturation- divisions, by
which the egg-cell and the sperm-cell prepare for their future
union in the process of fertilisation ? What is the good of
all these complicated arrangements ? Are they not perfectly
aimless ?
It is true that the two kinds of germ-cells are in their origin
essentially alike. This is proved, on the one hand, by the
embryonic development of the individual, in which the egg-
and sperm-cells proceed from similar germinal Anlagen and are
differentiated only at subsequent stages of development. It
is proved, on the other hand, by the phenomena of conjugation
in unicellular organisms, in which isogamy, i.e. the union of
two similar germ-cells, represents theoretically and practically
the first condition of propagation by germ-cells (see p. 132 on
Pandorina monim). Nevertheless, the differentiation of the
male and female germ-cells in the organic kingdom, and their
union in the normal course of fertilisation, are processes of the
highest teleological significance.
In order to see this more clearly, we must follow Boveri,
Weismann, E. Hertwig, Y. Delage, &c., in recognising a two-
fold object in fertilisation. (1) It aims at inciting to develop
a new individual, and (2) it aims at transmitting the combined
properties of both parents to this individual.
1. The first of these two aims can be realised both among
animals and plants by other means besides fertilisation. We
have seen this in the case of Infusorians and other unicellular
organisms, which increase either by simply splitting in two, or
by breaking up a colony of cells into single cells. Although
with them from time to time periods of conjugation have to inter-
vene between the periods of non-sexual or agamous multiplica-
tion, E. Hertwig's recent observations seem to show that there
is no direct connexion between conjugation and the multiplica-
tion of individuals by division. In multicellular animals and
plants, which are propagated by gemmation, we noticed that
OBJECTS OF FEKTILISATION 161
the new individuals come into existence independently of any
process of fertilisation. This is seen still more plainly in the
case of plants that can be propagated indefinitely by means of
cuttings and tubers, without weakening their growth, such as
the grape-vine and the potato. The absolutely sexless pro-
pagation of Laminaria and other plants bears witness to the
same fact, and natural parthenogenesis in animals and plants
shows that the development of a new individual from an egg
is not necessarily connected with its fertilisation.
In spite of all this, however, it cannot be denied that
where the normal process of fertilisation is the rule, it is of
great, even of essential, importance in realising the first of the
two aims of fertilisation, viz. in stimulating the formation of
a new individual.
According to Biitschli, the organic substance requires a
periodical rejuvenescence of its vital powers. The capacity
for growth and multiplication of cells is gradually weakened
and exhausted as life goes on, and eventually death from
senile decay must follow. But in order that the species may
not perish with the individual, it is necessary that certain cells,
viz. the germ-cells, of one individual should unite with those
of another in the process of fertilisation, that thereby their
vital force may be regenerated and renewed. There is certainly
much truth in this theory, although it has been vigorously
contested by Weismann in his ' Lectures on the Evolution
Theory ' (vol. i. pp. 325-328, English translation). His germ-
plasm theory leads Weismann to regard the germ-cells as
' potentially immortal,' and so he thinks there can be, in
connexion with them, no suggestion of senile decay calling for
rejuvenescence. But even Weismann does not venture to
deny that a strengthening of the metabolism or constitution of
the germ-cells is connected with fertilisation, and this differs
very little from an actual rejuvenescence of their vital force.
This is the reason why E. Hertwig1 has recently adopted
1 ' Uber Wesen und Bedeutung der Befruchtung ' (Sitzungsberichte der
Akad. der Wissenschaften, Munich, XXXII, 1902, pp. 57-73) ; * Uber Korrela-
tion von Zell- und Kerngrosse und ihre Bedeutung fur die geschlechtliche
Differenzierung und die Teilung der Zelle ' (Biolog. Zentralblatt, 1903, Nos.
2 and 3) ; ' tJber das Wechselverhaltnis von Kern und Protoplasma,' Munich,
1903 (reprinted from the Munchener Medizin, Wochenschri/t, I) ; ' Uber das
Problem der sexuellen Differenzierung ' ( Verhandl. der Deutschen Zoolog.
Gesellsch., 1905, pp. 186-214).
162 MODEEN BIOLOGY
Biitschli's theory under a somewhat modified form, and with
fresh evidence in support of it. Hertwig sees in the conjugation
processes of unicellular organisms, and in the phenomena
of fertilisation in multicellular, an important reorganisation
of their organic substance, and he lays particular stress upon
the restoration, by these means, of that relation between
nucleus and cytoplasm in the cell which is best adapted for
carrying on the vital functions.
Fr. Schaudinn's opinion approximates closely to Hertwig's.1
He thinks that the object of fertilisation is to restore the
proper equilibrium between the vegetative and animal proper-
ties of the organism ; he regards the egg-cell as the principal
bearer of the vegetative, and the sperm-cell as that of the
animal properties, because in the former the cytoplasm, and in
the latter the nucleus, predominates.
Whilst B. Hertwig and Fr. Schaudinn in their theories
emphasise particularly the physiological interaction of the
various constituents of. the cell, A. Buhler2has based a rejuj-
venescence theory of his own upon the chemical nature of the
metabolism in the living cells. He sums it up in the following
words : ' I have therefore arrived at the conclusion that, through
the act of fertilisation, something is again imparted to the new
organism which the old organism gradually lost in life and
through the processes of life, until its eventual death ; this
something being a molecular constitution of its parts, rendering
them capable of metabolism, and so fit to underlie all the vital
processes.'
From what has been already said on the subject it is
quite clear that there are very various views regarding the
rejuvenescence of the capacity of the germ-cells to develop,
especially in normal fertilisation. Let us therefore return to
the consideration of some of these theories.
According to Boveri and Strasburger, the centrosome of the
spermatozoon supplies the egg-cell with fresh kinoplasm,
whilst the trophoplasm of the egg-cell assists the sperm-
nucleus to develop. According to Y. Delage, the sperm-
1 ' Neue Forschungen iiber die Befruchtung bei Protozoen ' ( Verhandl. der
Deutschfin Zoolog. Gesellsch., 1905, pp. 16-35. and especially p. 33).
2 ' Alter und Tod ; eine Theorie der Befruchtung ' (Biolocj. Zentralblatt,
XXIV, 1904, Nos. 2, 3 and 4).
OBJECTS OF FEBTILISATION 163
nucleus renews the developing capacity of the egg-cell, by
taking away water from the egg-plasm, whilst the sperm-
nucleus grows into the male pronucleus precisely by absorbing
this water.
We must not overlook the fact that a rejuvenescence of
the developing capacity is probably connected with the matura-
tion-divisions of the germ-cells, but it presupposes the reunion
of the reduced and consequently rejuvenated nuclear substance
of both cells in the process of fertilisation, for the formation of a
new and particularly vigorous nucleus. If this union is not
effected, both cells generally perish, and no further develop-
ment results.
This seems to point to the fact that the nuclear union of the
two germ-cells in fertilisation must have some other, higher
purpose than the mere renewal of vital capacity in the single
germ-cells, for the differentiation of the germ-cells into egg-
and sperm-cells, and the physiological division of labour
connected with this differentiation, and the maturation-
divisions of both germ-cells all result in this — the egg-cell
alone and the sperm-cell alone are made incapable of further
independent development ; the new life of the embryo has to
proceed from their union. The object of this union is the
second of the objects of fertilisation that we have already
mentioned, viz. the transmission to the offspring of the com-
bined properties of both parents.1
2. This aim can in fact be attained only by fertilisation,
in the case of the higher organisms, or by the corresponding
processes of conjugation, in that of the lower organisms. In
agamous propagation the properties of one individual only
can be transmitted to its offspring, and the same is true of
unisexual propagation. The egg-cell that develops partheno-
genetically can transmit only maternal qualities to the new
creature, and in the same way, if we accept Boveri's observa-
tions on this subject as evidence, when non-nucleated egg-
fragments are fertilised, only the paternal sperm-nucleus is
the bearer of heredity. But in normal fertilisation, on the
contrary, both parents' properties, united or blended,
1 I need hardly point out that heredity is not in itself part of fertilisation,
for this is plain from the cases of non-sexual or unisexual propagation. Cf.
Reinke, Einleitung in die theoretische Biologie, pp. 413, 414.
M 2
164 MODEKN BIOLOGY
are transmitted to their offspring. This end is served by
all the morphological and physiological processes in the
germ-cells that prepare them for fertilisation, or take place
during it.
All modern cytologists are agreed in regarding the reduction
in the number of chromosomes in the mature germ-cells, the
restoration of the original number by the union of the chromo-
somes in the male and female pronuclei, and the even distribu-
tion of the paternal and maternal chromosomes at the cleavage
of the fertilised ovum, as constituting a process of great regula-
tive importance, to which we must ascribe an eminently
final teleological significance, as do E. B. Wilson1 and J.
Beinke.3 Let us begin by forming a clear idea of the process
of reduction by which the number of chromosomes in the
germ-cells is reduced to half.3
The reason for this is given by Weismann4 and by Oskar
Hertwig5 and others ; it is a process to prevent a summation
of the hereditary substances. Let n represent the number
of chromosomes constantly present in the somatic cells of
any definite species of animal or plant ; if no reduction took
place before fertilisation, the fertilised ovum and the somatic
cells developed from it in the next generation would each
contain 2n chromosomes, and the number would go on increas-
ing for ever in geometrical progression. As the chromosomes
of each species have a definite maximum size, fluctuating it 19
true within certain limits, it follows that in course of time
either all the somatic cells would consist exclusively of chromo-
somes, or the size of the cells, and consequently of the body
of the individual, would attain such huge dimensions, that
there would be no room for them in the world. Both con-
clusions are obviously absurd and quite chimerical. In the
first case we should have creatures more preposterously con-
structed than the fabulous Hydra, which consisted entirely of
| heads. In the second case we should have giants whose heads
I would touch the moon. Therefore, some kind of regular
1 The Cell, 1902, chapter v, pp. 233-288.
2 Einleitung in die theoretische Biologic, p. 442.
3 See pp. 110, &c. ; cf. also Korschelt and Heider, Lehrbuch der vergl. Ent-
wicklungsgesch., pp. 606-713 ('Wesen und Bedeutung der Chromatin-
reduktion ').
4 Lectures on the Evolution Theory, I, pp. 303, &c., Eng. trans.
6 Die Zelle und die Qewebe, I, Jena, 1892 ; II, Jena, 1898, chapter 9.
EEDUCTION OF CHKOMOSOMES 165
reduction in the number of chromosomes in the germ-cells
may be described as absolutely necessary.
But it would be quite possible for the numerical reduction,
accompanied by a corresponding quantitative diminution in
the amount of chromatin, to be effected in some other way
than that in which it actually occurs in the reduction processes
preparatory to fertilisation. It might take place after fertilisa-
tion by means of some regulative process, causing some of
the chromosomes to dissolve and be incorporated with the
protoplasm of the cell. This consideration has led Weismann,
0. Hertwig and others to conjecture that the processes of
reduction aim at the elimination of important factors in
organisation ; Weismann goes so far as to think that by
the reduction of chromosomes definite ' ancestral plasms '
are eliminated from the parental germ- cells. In other words,
according to these authors, whose views are now almost
universally accepted, numerical and quantitative reduction
of the chromatin is connected with a qualitative reduction.1
There is, however, great diversity of opinion as to the way
in which this is effected and its real significance. There are
even a few naturalists who, like Yves Delage,2 absolutely
question the expediency and the necessity of any such
qualitative reduction of the chromatin.
In spite of all these and many other difficulties and objec-
tions, we cannot avoid regarding as of great teleological
importance the fact that, before normal fertilisation, the
number of chromosomes in the germ-cells is regularly reduced
to half, and then is brought up again to the normal by means
of fertilisation. The maturation processes in the germ-cells
take place unmistakably in view of subsequent fertilisation.
Independently of it, they would be perfectly aimless, if not
actually harmful, because they render the egg-cell incapable
of further division, and so condemn it to death, if no fertilisa-
tion follows. This is still more true of the spermatozoon,
which in its whole structure is simply designed to be able
to fertilise an egg-cell. There must be some deeply signi-
ficant purpose hidden under these phenomena, and it is this :
The union of the nuclear substances of the egg- and sperm-cell
1 Cf. Korschelt and Heider, pp. 149, 712, &c.
2 Lea theories de la fecondation, p. 131.
166 MODEKN BIOLOGY
renders possible the transmission to the offspring of the
properties of both parents. The transmission of the combined
properties is effected in a very sure and simple way by the
reduction in the number of chromosomes in the two pronuclei,
by the union of the pronuclei in the process of fertilisation,
and by the regular distribution of equal numbers of paternal
and maternal chromosomes to the daughter-nuclei of the
dividing egg-cell.
As a matter of fact, both among animals and plants, the
force of heredity is as strong on the father's as on the mother's
side, although the sperm-cell often contains only one-
thousandth or one-hundred-thousandth part of the living
protoplasm contained by the egg-cell.1 This can be explained
only by assuming the nuclei of the two germ-cells, and especially
the chromosomes in the nuclei, to be the chief material bearers
of hereditary properties. Oskar Hertwig in 1898 2 pronounced
this to be his opinion, but as far back as 1884 he and Strasburger
declared the nuclear substance to be what Nageli called Idio-
plasm. Boveri, too, says very aptly on this subject : 3 ' However
widely the male and female germ-cells may differ, they
resemble one another in one point, viz. their nuclear substance.
The full-grown sperm-nucleus is indistinguishable from the
egg-nucleus, the paternal and maternal nuclear elements are
absolutely alike in size, shape, and number. All imaginable
care is shown in effecting their distribution in equal proportions
to the daughter-cells, and, as we may assume, to all the cells
of the embryo.4 In these paternal and maternal nuclear
elements must reside the directing forces, which stamp upon
the new organism not only the characteristics of its species,
but also the individual qualities of both parents combined.
This combination of the nuclear elements as means of trans-
mitting qualities would seem to be the object of all copulation
from that of the lowest Infusorians to that of mankind.'
In our task of considering the problems of fertilisation and
1 In one sea-urchin, Toxopneustes, the bulk of the spermatozoon is between
TOWOTT an(i sWo^i the volume of the ovum (Wilson, The Cell, p. 134).
2 Die Zetle und die Gewebe, II. 232, &c.
3 Das Problem der Befruchtung, p. 35. Cf. also 0. Hertwig, Allgemeine
Biologic, pp. 354, &c.
4 This applies especially to the cells in the germinal tract of the embryo.
Some deviation from this law may occur in the somatic cells, as part of
the chromatin loops is thrown off. Cf. pp. 123, &c., and p. 169.
INDIVIDUALITY OF CHROMOSOMES 167
heredity, we have here arrived at one important result, which
we can regard as fairly certain : Fertilisation consists
essentially in the nuclear union of two germ-cells, and through
this nuclear union the parental characteristics are transmitted
to the offspring. The chromosomes of the cell-nucleus are
shown in this process to be the immediate material bearers of
heredity in the organic world.
It is important once more to draw attention to the fact
that, in the nuclear union that takes place in fertilisation, the
chromosomes of the two pronuclei retain their individuality.
Whether — as in the Echinus -type ! — the male and female
pronuclei coalesce and form one common, resting cleavage-
nucleus, or whether — as in the Ascaris-type — the two pronuclei
remain distinct until they break up in forming the first cleavage-
spindle of the fertilised ovum : in both cases alike the paternal
and maternal chromosomes remain separate, divide themselves
independently, and distribute their longitudinal segments
equally between the two daughter-nuclei of the first cleavage
stage of the ovum. This independent action on the part of
the chroma tin derived from father and mother respectively
may, as V. Haecker2has shown, be traced in favourable cases
from the nucleus of the fertilised ovum, through numerous
generations of cells, to the nuclei of the germ-cells in the
embryo resulting from this fertilisation. This independence
of the chromatin elements is what Boveri calls < the in-
dividuality of the chromosomes ' ; to some extent it stamps
these morphological constituents of the cell as being the
visible bearers of heredity.
Boveri's well-established hypothesis of the individuality of
the chromosomes3 has been accepted in the last few years,
1 See pp. 120 and 156 for the difference between these two types of fer-
tilisation.
2 ' Uber die Autonomie der vaterlichen und mutterlichen Kernsubstanz
vom Ei bis zu den Fortpflanzungszellen ' (Anatomischer Anzeiger, XX, 1902).
Rabl, Boveri, and Riickert have made similar observations. Cf. Wilson, The
Cell, p. 208 ; O. Hertwig, Allgemeine Biologic, pp. 289, &c.
3 On the subject of Boveii's theory of the individuality of the chromosomes,
see his lecture on the problem of fertilisation (Das Problem der Befruchtung,
Jena, 1902), and also the following works by the same author : ' Uber
mehrpolige Mitosen als Mittel zur Analyse des Zellkerns ' (Verhandl. der
physikal.-medizin. Gesellschaft., Wiirzburg, XXXV, 1902, pp. 67-90); ' Uber die
Konstitution der chromatischen Kernsubstanz ' ( Verhandl. der Deutschen
Zoolog. Gesellsch., 1903, pp. 10-33); ' Ergebnisse iiber die Konstitution der chro-
matischen Substanz des Zellkerns,' Jena, 1904. In the last-named work Boveri
168 MODERN BIOLOGY
not only by most zoologists, but also by eminent botanists,
such as E. Strasburger1 and J. Keinke;2 others, however,
such as Yves Delage, have opposed it, whilst it has been only
partially adopted by E. B. Wilson ('The Cell,' pp. 294-301) 3
and Oskar Hertwig (' Allgemeine Biologie,' 1906, pp. 205-208).
Should it be fully confirmed, our comprehension of the material
basis of heredity would undoubtedly be facilitated. According
to Boveri, the chromosomes during karyokinesis are in a
state of rest, and in this condition they have clearly defined
shapes and are strongly susceptible to nuclear stains, which
render them visible in fixed numbers. When the fresh nuclei
of the daughter- cells are formed, the chromosomes in them
revert from a state of rest to one of activity, in which they
control all the vital functions of the cell. Their free ends
approach one another, unite and become matted together
by means of amoeboid processes, so that they form a coil of
chromatin thread or a chromatin network. It is not until
the next division of the cell that the chromosomes reappear
in the same form, number, and order as before, in fact, in the
same ' individuality ' ; they are again separate, just as the
oxygen and hydrogen which make up water are given off
again when the water is resolved into its chemical constituents.
In the case of chemical compounds, we may assume persistence
in the elements of which they are composed, and, in exactly
the same way, we may assume a similar latent persistence of
formulates his theory most precisely. A good account of the development of
the theory of individuality up to 1900 is given by Wilson, The Cell, pp. 294-301.
Fresh confirmation of it, in a department where it was formerly contested, is
added by J. Marechal, ' t)ber die morphologische Entwicklung der Chromo-
somen im Keimblaschen des Selachiereis ' (Anatomischer Anzeiger, XXV, 1904,
Nos. 16 and 17, pp. 383-398) and ' Uber die morphologische Entwicklung der
Chromosomen im Teleostierei ' (ibid. XXVI, 1905, No. 24, pp. 641-652). That
the chromosomes are not to be regarded literally as individuals is obvious,
and Boveri himself does not mean this ; he considers only that they are
clearly denned parts of the cell, capable of independent division and
redintegration.
1 ' tiber Reduktionsteilung ' (Sitzungsber. der Berl. Akad. der Wissensch.,
XIV, 1904, pp. 587-614). Cf. p. 116.
2 Philosophic der Botanik, 1905, pp. 60, 69, 70, 143.
a Wilson is of opinion that not the chromosomes themselves, but only their
constituents, the chromomeres, remain as constant elements through all
changes in the nucleus. , It is, therefore, to the chromomeres that we ought
to ascribe ' individuality,' rather than, as Boveri does, to the chromo-
somes. For our purpose it is, however, a matter of indifference whether the
chromosomes or the chromomeres should eventually be proved to possess
individuality.
INDIVIDUALITY OF CHROMOSOMES 169
the chromosomes as the material bearers of the laws of organic
development during the whole life of the cell.
On p. 166 I quoted Boveri's statement to the effect that
in the cleavage-divisions of the fertilised ovum the chromo-
somes of the cleavage-spindle are distributed in equal propor-
tions to all the cells of the embryo. The exceptional cases,
to which I have already referred shortly (pp. 123, &c.), con-
firm Boveri's opinion that the chromosomes possess a certain
individual independence. At the cleavage of the ovum
of Ascaris megalocephala var. bivalens, from the two-cell stage
onwards, the four chromosomes of the cleavage-spindle remain
only in those daughter- cells which are to supply the germ-
cells of the embryo, whereas they undergo a striking modifica-
tion in those daughter-cells which are to produce the somatic
cells. In these the ends of the chromosomes are cast off and
lost, and the remaining middle-piece breaks up into a number
of little rods (see p. 124, fig. 23). In subsequent divisions,
giving rise to somatic cells, the chromosomes always appear
in this form and order, but in the cells of the germinal area
the original number, form, and arrangement of the chromo-
somes are preserved, until finally, before the maturation-
divisions of the germ-cells, the ordinary chromatin reduction
occurs, and the number of chromosomes is reduced to half,
and then is brought back to the normal by fertilisation. In
biological language this morphological result is stated thus :
The chromosomes of the germinal areas represent in an
unbroken series the bearers of heredity for the species in
question. In a series of observations made in 1901 on a
water-beetle, Dytiscus, Giardina1 has described processes
which show a difference in the nuclei of sexual cells and somatic
cells. Here, too, in the former chromatin elements remained
constant, which were lost in the latter.
Some recently discoveredjfacts pointing to a qualitative
difference in the chromosomes^of one and the same nucleus are
very significant.3 It is enough for the present to say that
in the spermatogenesis of various insects (especially in bugs,
beetles, and grasshoppers) a so-called superfluous or accessory
1 ' Origine dell' oocite e delle cellule nutrici nel Dytiscus ' (Internat. Monat-
schr, fur Anatomic und Physiologic, XVIII, 1901).
2 Boveri gives a short summary of them. ' Uber die Konstitution der
chromatischen Kerasubstanz,' pp. 20-26.
170 MODEBN BIOLOGY
chromosome occurs,1 which at the last maturation- division
passes undivided into one of the two sperm-cells, whilst the
other receives one chromosome less. Montgomery calls these
accessory chromosomes heterochromosomes ; he has observed
them in the spermatogenesis of spiders.2
Button noticed, in the spermatogenesis of a grasshopper —
Brachystola magna — (1900 and 1902), that in the secondary
spermatogonia (descendants of the male germ-cells) not only
did the extra chromosome appear regularly for nine generations
of cells, but the other chromosomes of the same cells fell into
two groups of different sizes, and always occurred in pairs.
Quite recently E. B. Wilson has made a very careful study of
the qualitative differences of the chromosomes in the germ-
cells of bugs (Hemiptera), and their biological functions.3
He distinguishes normal chromosomes, or idiochromosomes,
from abnormal or heterotropic (accessory) chromosomes.
The idiochromosomes are of two sizes, which he calls respec-
tively macrochromosomes and microchromosomes ; they
occur either in pairs or singly. In the egg-cells the mature
ova invariably contain half the normal number of chromo-
somes, but among the sperm-cells there are three different
types, with chromosomes varying in quality or quantity.
Wilson attempts to account for the sex differences in Hemiptera
as depending upon the different combinations of these male
chromosomes with the female.
When we consider that Mendel's Law of Hybridisation,4
1 For a fuller account of it see Wilson, The Cell, pp. 271, 272 ; Korschelt
and Heider, Vergleichende Entwicklungsgesch. der wirbellosen Tiere, Allgem.
Teil, pp. 599-601 ; B. de Sinety, Recherches sur les Phasmes, 1901,
pp. 123-126 ; Sutton, ' The Spermatogonial Divisions in Brachystola magna '
(Kansas Quarterly Journal, 1900 and 1902) ; J. Pantel and R. de Sinety, * Les
cellules de la lignee male chez le Notonecta glauca ' (La Cellule, XXIII, 1906,
fasc. I. pp. 89-303, 138, &c., 245). See also the works mentioned on p. 110,
note 2.
2 T. H. Montgomery, ' Spermatogenesis of Syrbula and Lycosa, with general
remarks on the reduction of Chromosomes and on Heterochromosomes '
(Proceedings Acad. Nat. Science, Philadelphia, LVII, 1905, pp. 161-205).
Montgomery classes as heterochromosomes all those that differ from the
normal in size or structure. Cf. on this subject a review in the Naturwissen-
schaitliche Rundschau, 1906, No. 4, p. 44.
3 ' Studies on Chromosomes,' I, II, and III (Journal of Experimental
Zoology, 1905, Nos. 3 and 4 ; III, 1906, No. 1).
4 Greg or Mendel (1822-84) was abbot of the Augustinian monastery in
Briinn. Cf. C. Correns, 'Gr. Mendels BriefeanC. Nageli,' 1867-73 (Abteil. der
mathemat.-physikal. Klasse der Kgl. Sdchsischen Gesellsch. der W issenschaften
XXIX, 3, 1905). Mendel's laws of segregation are dealt with very fully
MENDEL'S LAW 171
which is to a great extent confirmed by the phenomena of
hybrid fertilisation, may have a quite^simple morphological basis,
if we accept Boveri's theoryof the individuality of chromosomes
(as Boveri himself was the first to show),1 we can scarcely
refrain from ascribing to the chromosomes a certain individual
independence, in virtue of which they become the material
bearers of heredity. At the seventy- seventh meeting of
German naturalists and physicians at Meran in September 1905,
the interesting connexion existing between the individuality
of the chromosomes and Mendel's Law was discussed by
C. Correns from the botanical point of view,2 and by C. Heider
from the zoological and cytological.3 I must limit myself
here to a very brief account of the matter.
Mendel's Law of Hybridisation, which has recently
attracted so much attention, comprises three rules : the rule
of dominance, the rule of segregation, and the rule of independ-
ence of characters. According to the rule of dominance, when
two sub-species (e.g. red and white peas) are crossed, the hybrid
offspring of the first generation resemble one parent (the white
pea) in every respect, and the characteristics of the other
parent (the red pea) do not show themselves. The character
that appears in the first hybrid generation is called the dominant,
and the contrasted character that disappears is called the
recessive. According to the rule of segregation, if the breeding
of these hybrids be continued, the contrasted characters of
both parents are again distinguished or segregated, and in such
a way that half the germ-cells of the hybrid tend to give
rise to the character of one parent, and the other half to the
character of the other parent. According to the rule of
independence of characters, the various individual characters,
by de Vries, in the second volume of his Mutationstheorie, 1903, and by Lotsy
in his Vorlesungen uber Deszendenztheorien, 1906, Lecture 8. They have been
applied to cross-breeding among silkworms by K. Toyama, ' Mendel's laws
of heredity as applied to the silkworm crosses' (Biolog. Zentralblatt, XXVI,
1906, Nos. 11 and 12). Cf. also J. Gross, ' Uber einige Beziehungen zwischen
Vererbung und Variation ' (ibid. Nos. 13-18). According to Gross (p. 414)
no typical instances of Mendelism occur when species are crossed.
1 uber die Konstitution der chromat. Kernsubstanz, pp. 32-33. J. Reinke too
thinks (Einleitung in die theoretische Biologie, p. 539) that Mendel's law supports
the theory that the chromosomes are the chief bearers of heredity.
2 * Uber Vererbungsgesetze ' ( Verhandl. der 77 Versammlung deutscher
Naturi. und Arzte, Leipzig, 1906, Part I, pp. 201-221).
3 4 Vererbung und Chromosomen ' (ibid. pp. 222-244).
172 MODEKN BIOLOGY
which' [distinguished the parents of the first hybrid, appear
quite ^independently of one another, when cross-breeding is
continued.
When two sub-species of the same species are crossed, and
the characters of the offspring follow Mendel's laws, they are
said to ' mendelise.' Mendel formulated his law in consequence
of experimental observations on hybridisation, and quite apart
from microscopic research. Working, however, on other lines,
cytologists have found three important principles, which lead
them to regard the chromosomes as the material bearers of
heredity and to ascribe to them a certain individual independ-
ence. Firstly, each germ-cell receives exactly half the normal
number of chromosomes, and of those which it contains, half
are paternal and half maternal. Secondly, each germ-cell
receives the total number of chromosomes necessary to normal
development, these chromosomes being parental in origin, but
qualitatively different. Thirdly, these chromosomes may
meet in the germ-cells of the offspring in very various com-
binations (arranged mostly in tetrads or groups of four), and
there they form regularly fresh combinations in their matura-
tion-divisions and fertilisation.
If we may assume that qualitatively different chromosomes
are the bearers of definite hereditary qualities, these three
principles will enable us easily to explain, not only Mendel's
three rules, but also most of the other phenomena of variation
and heredity.
Of the numerous instances quoted by Correns and Heider
in the above-mentioned lectures, I may give one by way of
illustration.
A red and a white specimen of Mirdbilis Jalapa were
crossed. The hybrids of the first generation all bore pink
blossoms,1 those of the second generation were partly white,
partly red, partly pink, in the ratio 1:1:2; so that the
pink blossoms were twice as numerous as either the white or
the red. Let us assume (see Plate II) that the tendency to
produce red blossoms is represented by a definite chromosome
1 According to Mendel's rule of dominance the red colour of one parent
ought to have been the dominant, but this was not the case. The rule of
dominance, therefore, is not illustrated by this example, and it is more difficult
to account for it by the chromosome theory than for the rule of segregation.
On this subject see p. 173, note 2, of Gross's work.
MENDEL'S LAW 173
A, and the tendency to produce white blossoms by a definite
and qualitatively different chromosome a. The red variety
of Mirabilis Jalapa has among its chromosomes only A, the
white variety only a, as influencing the colour of the blossom.
The first hybrid generation receives in its fertilised egg-cell
and in all the somatic cells the combination A-|-a, i.e. all its
blossoms are pink. At the maturation-divisions of the germ-
cells of this first hybrid generation a separation of the A -|- a
pair of chromosomes takes place, and by the reduction processes
half of all the mature germ-cells receive chromosome A, and
the other half chromosome a. What is the result to the
second generation, produced by the union of these germ-cells
in twos ? In the somatic cells the chromosomes will be thus
combined, A-f-A, A+a, a+A, a-\-a, and each combination
will probably occur the same number of times ; in other words,
in this generation there will be pink blossoms as well as pure
red and pure white,but the pink will be about twice as numerous,
which was actually found to be the case. Plate II at the end
of the book illustrates this relation of the chromosome theory
to the phenomena of hybridisation. The diagrams were used
in Heider's lecture.
We have now learnt to regard the mixture of qualities as the
chief aim of fertilisation, in which the combined properties of
both parents are transmitted to their offspring, and we have
seen further that the chief part in this transmission is played
by the chromosomes of the cell-nucleus. The next question we
must answer is this : What is the object of this blending of
qualities ? Why is it of so much importance to the main-
tenance of organic species that Nature has taken great
pains to secure it, by means of these complicated and regular
arrangements ?
The opinions held on this subject are to some extent con-
tradictory. We may safely take it for granted that the
rejuvenating or regenerating effect, ascribed by Biitschli,
K. Hertwig, A. Biihler and others to the process of fertilisation,
is due, at least in part, to this blending of qualities. But I
have already referred to their theories (pp. 162, &c.), and so we
need now only answer the question : What is the significance
of blending qualities for the race development of different
species ? Does it act in a conservative or in a liberal sense ?
174 MODERN BIOLOGY
Does it promote permanence of species or does it supply the
means of altering them ? l
Charles Darwin, Spencer, Romanes, Hatschek, 0. Hertwig
and others have regarded this blending of parental qualities
effected by fertilisation as a means of compensating for
individual fluctuations ; they are therefore of opinion that
this union of qualities preserves the purity of the race, and so
makes for permanence.
According to these authors it would be possible for a new
variety, race, or species to arise only if the possibility of breeding
with individuals of the same species were restricted, by either
exterior or interior circumstances, to definite and limited
groups of individuals, which then had the power to propagate
and intensify their peculiarities. On this idea are based
Wagner's theory of migration, Romanes' theory of physiological
selection, Gulick's theory of segregation, &c.
August Weismann's view is, however, directly opposed to all
these.3 He thinks that amphimixis, i.e. the mixing of qualities
resulting from fertilisation, is the chief means of modifying
species. It gives rise to fresh combinations of the nuclear
elements, and to corresponding new variations in the hereditary
qualities of the offspring. These variations offer a wide field
for natural selection, which ' breeds ' from them new races and
species.
At first sight this theory is very attractive. Let us assume
that the male and female pronuclei of the germ-cells of some
organic species possess each eight chromosomes before their
union in the process of fertilisation, and that these sixteen
chromosomes differ qualitatively from one another. In the
cleavage-spindle of the fertilised ovum they may be paired in
no less than sixty-four different ways, and so may produce
sixty-four descendants, all differing qualitatively from one
another and from their parents. Now, as a matter of fact, in
most species of plants and animals the number of chromosomes
is far higher than sixteen,3 and therefore the possible number
of variations due to fertilisation is correspondingly higher.
It appears to be true that by blending qualities a very vast
1 See Korschelt and Heider, Lehrbuch der vergl. Entwicklungsgesch., pp. 702, &c.
2 Lectures on the Evolution Theory, I, pp. 331, &c.; II, pp. 192-237 (Eng. trans.).
3 See Chapter V. pp. 92 and 93.
AMPHIMIXIS 175
field is opened to natural selection. Boveri agrees with
Weismann to a certain extent,1 and thinks that the mixture
of qualities, which is the chief object of fertilisation, is one
means, and even one of the most efficacious means, whereby
organic species have developed from the simplest Protozoa to
the highest animals and plants.
My own opinion nevertheless is, that the amphimixis
resulting from fertilisation may not be of such importance to
the evolution theory as Weismann believes.3 I need not now
lay much stress on the many objections to it that can be
raised. For instance, it is quite common to find the number
of chromosomes differing greatly in closely connected species
of animals and plants — e.g. in the Ascaris class of worms —
whilst forms as far removed from one another as the frog,
the salamander, the mouse, the salmon, a crab (Branchipus),
a bug (Pyrrhocoris) and the lily all have the same number
of chromosomes, viz. twenty-four. Some experimental
evidence is needed to show that the variability of the
species is directly connected with, and dependent upon,
the number of its chromosomes. Weismann anticipated
these difficulties by suggesting, in his theory of determinants,
that only the larger complexes of bearers of heredity (the ids)
correspond to the chromosomes ; each of these is built up of a
great number of smaller bearers of heredity (determinants),
which are equivalent to the chromomeres or smallest grains
of chromatin in the chromosomes, and are able to vary in-
dependently of one another. As very little is actually known
of the finer structure of the chromosomes,3 these theoretical
speculations cannot be tested by means of microscopical
research.
There are, however, other objections to Weismann'a theory
of the importance of amphimixis, and they are, perhaps, of
greater weight. We must notice at the outset that indiscri-
minate cross-breeding between individuals of the same species
1 Das Problem der Befruchtung, pp. 36-38.
2 We must be careful to distinguish amphimixis in Weismann's sense,
in which it refers to the blending of qualities of individuals belonging to the
same species, from the other use of the word, in which it refers to sexual cross-
breeding between individuals of different species. I shall discuss the latter
kind of amphimixis, as bearing upon the Evolution theory, in Chapter IX,
' Theory of permanence or theory of descent.'
3 Wilson, The Cell, pp. 301, 302.
176 MODEKN BIOLOGY
can never lead to a new permanent variety, ag the average
will always recur. Moreover, a completely new quality in the
offspring can never be produced by a mere combination of
qualities present in the parents. It is therefore difficult to see
how a mixture of qualities can ever give rise to new species,
families, classes, &c., in which some new organ or system of
organs is frequently the distinguishing characteristic. Natural
selection is, according to Weismann, the sole directive element
in the evolution of a race, but all that it can do is to make
choice out of the variations furnished by amphimixis, and to
preserve the individuals best capable of existence, and therefore
Weismann's whole theory of evolution seems unsatisfactory ;
mere amphimixis and selection could never have produced
the present system of animals and plants from extremely
simple primitive organisms.
Since 1895 Weismann has very ingeniously tried to meet
this objection by bringing forward his theory of germinal selec-
tion as a new factor in evolution. He now no longer regards
the determinants of hereditary qualities in the nuclear substance
of the germ-cells as invariable, but is of opinion that they
1 are continually oscillating hither and thither in response
to very minute nutritive changes, and are readily compelled to
variation in a definite direction, which may ultimately lead to
considerable variations in the structure of the species, if they
are favoured by personal selection, or at least if they are not
suppressed by it as prejudicial.' l
He goes so far as to speak of ' vital affinities/ 2 i.e. of definite
interior forces uniting the determinants into ids, and the
biophors into determinants. It is undoubtedly a very interest-
ing concession on Weismann's part, when he says : 3 'In all
vital units there are forces at work which we do not yet know
clearly, which bind the parts of each unit to one another in a
particular order and relation.' Weismann seems here to
acknowledge that it is impossible ever to understand a develop-
ment of the organic world, with definite arrangement, and
consequently ordered in conformity to law, unless there are
interior laws governing that development. If — as Weismann
1 Weisinann, Evolution Theory, II, p. 196, Eng. trans.
2 Ibid. I, p. 374 ; II, p. 36.
3 Ibid. II, p. 35.
VITAL AFFINITIES 177
suggests in these quotations — there is a connexion, tending
to some aim, between the material bearers of heredity among
themselves and the influences of the outer world, so that the
former are modified by the latter and directed into new channels
of development, he seems also to grant that there is a_teleological
element in the constitution of these material bearers of heredity,
to which they own their capacity to adapt themselves to new
circumstances by corresponding changes in their constitution,
and thereby to effect a regular development of the organic
species.
This teleological element, which I have described as the
interior laws governing the development of organisms, is no
1 mystical, intangible thing ' hovering vaguely in the air, as
some of my opponents have imagined. It is the original
chemico-physical and morphological constitution belonging to
the first bearers of the hereditary qualities of the race, at least
in its material aspect. If we wish to explain the phenomena
of heredity, we must consider in this material constitution
not only the morphological character of the smallest and most
elementary parts of living substance, that make transmission
of qualities possible, but also their dynamic and physiological
action.1
It cannot be denied that we need moreover some formal
principle to explain these laws of evolution. J. Keinke, the
well-known botanist, has lately acknowledged this, by declaring
the chromosomes of the nucleus to be the chief agents-, in all
probability, in transmitting specific dominants.3
Hans Driesch,3 one of the best and most thorough students
of organic development, seems to hold a very similar opinion,
for he says that the processes of organic development require,
1 On this subject see J. Reinke, Philosophic der Botanik, Leipzig, 1905,
p. 106 ; 0. Hertwig, Allgemeine Biologic, 1906, chapter xii, ' Die Physiologie
des Befruchtungsprozesses.' From what is stated above and also from what
follows, it is plain that Gemelli, in his Italian translation of the last edition of
this work (Wasmann-Gemelli, La Biologia moderna, 1906, pp. 218-221), com-
pletely misunderstands me, if he thinks that I regard the chromosomes as a
transmitting substance in a purely morphological sense.
2 Cf. J. Reinke, Einkitung in die theoretische Biologic, 1901, p. 455 ; see also
pp. 386-408 and especially p. 396. Cf. further his Philosophic der Botanik,
1905, pp. 53, &c., pp. 71, &c.
3 Of his works cf. especially the following : Die organischen Eegulationen ;
Vorbereitungen zu einer Theoric des Lebens, Leipzig, 1901 ; Die Seele als
elementarer Naturfaktor, Leipzig, 1903 ; Kritisches und Polemisches
(Biolog. Zentralblatt, 1902, Nos. 5, 6, 14, 15 ; 1903, Nos. 21, 22, 23).
178 MODEEN BIOLOGY
as an indispensable directive power, a teleological formal
principle which may be compared with the entelechies. If
this is true for the development of the individual, we may
regard it as still more necessary for the hypothetical develop-
ment of the race. I shall recur to this topic at the close of
Chapter VIII ( ' The Problem of Life ' ), and in the course
of Chapter IX ( ' Thoughts on the Theory of Evolution ').
From the evidence given in the present chapter it appears
that we may, with great probability, regard the chromosomes
of the nuclei in the germ-cells as the chief material bearers of
heredity.1
We have now obtained a scientific foundation for the
interior laws of development, which are the necessary premiss
for the hypothesis of a race evolution of organic species. I
shall have to deal with this hypothesis in a subsequent chapter :
' Thoughts on the Theory of Evolution.' For the present I will
only draw the reader's attention to the fact that all the results
of modern biological research, in this department as in others,
increase our appreciation of the Creator's wisdom and power,
and show us in what a simple and yet wonderfully regular way
the transmission of the parents' qualities to their descendants
is effected, by means of most diminutive material portions of
the germ substance.
1 Further information of great interest, and tending to confirm this theory,
may be found in C. Correns' lecture Uber Vererbung (On Heredity) and
C. Heider's Vererbung und Chromo&omen (Heredity and Chromosomes).
These lectures, to which I have referred on p. 171, were delivered in September
1905, at the seventy-seventh meeting of German naturalists at Meran.
CHAPTEK VII
THE CELL AND SPONTANEOUS GENERATION
1. THE CELL AS THE ULTIMATE UNIT IN ORGANIC LIFE.
There are no organisms more simple in construction than the cell (p. 180).
Bathybius (p. 181). Monera (p. 181). Absence of nucleus in
Bacteria (p. 182). Non-nucleate red blood-corpuscles (p. 185). Free
nuclear formation (p. 186). The cell not composed of lower
elementary units (p. 187). The idea of individuality in unicellular
and multicellular creatures (p. 188). Energids (p. 189). Survey
and criticism of the hypothetical living units of the lowest rank
(p. 190).
2. SPONTANEOUS GENERATION OF ORGANISMS.
What is spontaneous generation ? (p. 193). Untenable character of
the chemico-physical theories of spontaneous generation (p. 195).
Radium and spontaneous generation (p. 197). Untenable character
of the biological theories of spontaneous generation (p. 198).
History of the theory (p. 199). Gradual refutation of the
theory by modern biology (p. 201). Theory of spontaneous genera-
tion not a postulate of science (p. 204). Theory of creation a true
postulate of science (p. 206).
I HAVE already shown (Chapter III, pp. 55, 65, &c.) that the
cell is not a simple entity, but a compound formation of very
delicate and artistic structure, as recent research has proved.
We have also considered the life of the cell (Chapter IV) and
convinced ourselves of the great and universal importance
of the nucleus in every function of cellular life, but especially
in cell-division and in the processes of fertilisation (Chapters
V and VI). We have now sufficient material at our disposal to
enable us to answer with assurance the question propounded
long ago : ' Is the cell the ultimate unit of organic life, or is it
merely an aggregation of still more elementary units ? ' The
solution of this problem will help us to form a really scientific
opinion on spontaneous generation or generatio aequivoca, for
almost all attempts to disprove the unity of the cell have been
motived by a desire to make the origin of organic life in the
world more intelligible by the assumption of spontaneous
generation.
179 N2
180 MODEKN BIOLOGY
1. THE CELL AS THE ULTIMATE UNIT IN ORGANIC LIFE
The question of the unity of the cell resolves itself into two
other questions, which we shall answer each in turn. The
first is : * Are there really in nature organic entities of a still
lower organisation than the cell ? ' The second is : 'Do the
morphologically different elements of the cell form together
one biologically indivisible unit, or can they be divided into
subordinate biological units ? ' On the answers which facts
supply to these questions, depends our acceptance of the
various theories which represent the cell as a mere aggregation
of lower units, or our rejection of the same as fictions. What
does recent research tell us as to the existence of living entities
of still lower organisation than the cell ? It has really answered
this question plainly enough already ; it has shown us that
the cell-nucleus is also the principle of organisation for the
living cell, directing its most important vital activities, and,
by means of heredity, maintaining the continuity of organic
life. Consequently we should expect to find no organism with
a protoplasmic body containing no nucleus, and none with a
nucleus that is not inserted, or meant to be inserted, in a proto-
plasmic body.
This does not, however, prove that in all organisms the
cell-nucleus must be developed in equal perfection. On the
contrary, the graduated perfection of organic beings may
extend also to the organisation of the cells, and we need not
be surprised to find, even among the lowest living creatures,
some in which the nucleus is not formed into one morphological
whole, but is scattered in little grains of chromatin (chromidia)
about the protoplasm of the cell. As we shall see directly,
this occurs, apparently at least, in many Bacteria. In Chapter
III, p. 49, I pointed out that the nucleus was essential to
the existence of the cell, either in a complete and centralised
form, or in a diffused and incomplete one. This latter state-
ment need not surprise us, as we have seen, in Chapters V and
VI, that during indirect cell- division the distinct nucleus
ceases for a time to exist as such, because the nuclear membrane
breaks up and the chromatin framework of the nucleus divides
into small pieces, viz. the chromosomes, and is only reorganised
NON-NUCLEATE OKGANISMS 181
in the newly formed nuclei of the daughter-cells. The sharply
denned form of the nucleus is not therefore essential to the
cell, although the presence of the nuclear substance is essential.
Attempts have been made to demonstrate the existence of
really non-nucleate primitive organisms, or at least to assert
the possibility of their existence. Let us examine them in
order and test their value.
For a short time it was believed that the long- sought
organic matter, devoid of all structure, which Ernst Haeckel
announced as the Promised Land of Darwinism, had really
been discovered. The discovery was made whilst the North
Atlantic cable was being laid in 1857. Huxley subsequently
described this primitive matter as consisting of little organic
masses, without nucleus and without any structure, found
at the bottom of the ocean, and named by him Batkybi'&s
Haeckelii, after the famous prophet of Darwinism. But the
godfather himself was obliged later on to declare this hopeful
scion of the Evolution Theorj^ to be a changeling, foisted upon
him by an impish trick of bad luck. He had to withdraw his
discovery, and acknowledge that there had been a mistake,
about the Bathybius. It was nothing but a deposit formed
accidentally in a test-tube filled with alcohol. Bessels, the
explorer of the North Pole, afterwards thought that he had
rediscovered the primitive organism, which he called Proto-
bathybius ; but in spite of the amoeboid movements that he
said he observed, the ProtobatJiybius^ has not yet been admitted
to the rank of a living creature ; at best it appears to be a
deposit of organic substance which has formed at the bottom
of the sea from the remains of plancton organisms. Haeckel's
own creations, the ostensibly non-nucleated Monera, still de-
mand consideration. Haeckel classed together as Monera,
the lowest division of Protozoa, all those that he thought
contained no nucleus. Their number seemed at first to be
legion, and to justify the hopes set upon them by the advocates
of the Evolution Theory. But as our microscopes and our
methods of research were improved, they melted away like
snowflakes in the sunshine. Apochromatic objectives and
modern staining methods have revealed the hitherto obscure
nucleus in almost all Protozoa, and all possessors of a nucleus
were at once banished from the class of Monera, which grew
182 MODEKN BIOLOGY
smaller and smaller. The day is not far distant when the last
Moneron will share the fate of the last of the Mohicans. On
this subject we may refer to R. Hertwig, an eminent zoologist
and a favourite pupil of Haeckel's. In the seventh edition of
his ' Lehrbuch der Zoologie '(1905, p. 159), he writes as follows :
' The most important feature in the Monera is said to be the
lack of a nucleus. Like every negative characteristic, this is
somewhat unsatisfactory. In many cases it is difficult to
recognise nuclei, especially when the protoplasm is abundant
and filled with chromatin granules, and thus it may happen
that animals are described as devoid of nucleus, simply because
the existing nucleus has been overlooked. For this reason the
number of " Monera " was at one time very large ; it has
diminished, as improved technical methods have revealed
nuclei, and so it is not only possible, but even probable, that,
in the few forms still reckoned as Monera, the nuclei have only
escaped notice ; perhaps their functions are discharged by
chromidia.'
Unicellular animals without a nucleus have therefore no
longer any scientific justification for existence ; and no one
can refer to them as affording evidence of there being living
creatures of a still lower degree of organisation than cells
possess. It may, however, be asked : Can the long-sought
non-nucleated forms be discovered amongst the lowest plants ?
Botanists are still not agreed as to the presence of a genuine
cell-nucleus in Bacteria and Cyanophyceae, to which the
Oscillaria also belong.1
Biitschli thought that he had discovered in Bacteria a very
large nucleus, not clearly marked off from the layer of cyto-
plasm, but Fischer contradicted this statement. Arthur Meyer
(' Flora,' 1899, pp. 428, &c.) believed that several little nuclei
could be traced in the cells of some Bacteria. Fritz Schaudinn
1 For the bibliography of this subject, see Strasburger, Lehrbuch der Botanik,
sixth edition, 1904 ; Biitschli, Weitere Ausfuhrungen uber den Ban der Cyano-
phyceen und Bakterien, Leipzig, 1896 ; Fischer, Untersuchungen uber
den Ban der Cyanophyceen und Bakterien, Jena, 1897 ; G. Schlater, ' Zur
Biologic der Bakterien: Was sind Bakterien?' (Biolog. Zentralblatt, . 1897,
pp. 833, &c.) ; J. Reinke, Einleitung in die theoretische Biologie, Berlin, 1901,
chapter 25, pp. 256, &c. ; R. Hertwig, ' Die Protozoen und die Zellentheorie,'
Archiv fur Protistenkunde, I, 1902, pp. 1-40) ; Fr. Schaudinn, ' Beitrage zur
Kenntnis der Bakterien und verwandter Organismen ' (Archiv fiir Protis-
tenJcunde, I, 1902, pp. 306, &c. ; II, 1903, pp. 421, &c.).
NON-NUCLEATE OKGANISMS 183
has discovered quite recently that in the case of Bacillus
Butschlii, a large parasitical fission fungus found in the intestine
of the cockroach, Periplaneta orientalis, a genuine nucleus
appears temporarily during the formation of spores, although
otherwise the nuclear substance is dispersed in the cell. K.
Hertwig's investigations into Bacteria and Oscillaria have
led him to conclude that these organisms ought to be regarded
as cells without a clearly differentiated nucleus, but having
the nuclear substance distributed among the protoplasm.
He gives the name chromidia to the little particles of chromatin
in Bacteria, corresponding to the chromosomes and their
constituents, the chromomeres, in true nuclei.
J. Keinke does not venture to express a general opinion
as to the non-nucleate character of Cyanophyceae and Bacteria,
but he considers that the cell of Beggiatoa, a tiny, thread-
like Bacterium, is non-nucleate to this extent, that it does
not contain any distinct nucleus, in the sense in which the
higher plants and animals contain nuclei.
In the sixth edition of his * Lehrbuch der Botanik,' p. 46,
Strasburger says : ' The two most essential constituents of
the protoplasm (i.e. of the living cell) are the nucleus and the
cytoplasm, and the vital functions of the cell depend upon
the interaction between them. But in the lowest plants,
Cyanophyceae and Bacteria, the existence of a nucleus is still
uncertain.' On p. 270 of the same book, Schenk, in writing
of Bacteria, remarks : ' In the protoplast there are one or
more granular structures called chromatin-bodies, which
may be deeply coloured by stains, and are regarded as nuclei
by various authors. Hitherto no one has succeeded in
demonstrating undoubted karyokinesis in them, and therefore
the presence of nuclei (in Bacteria) is still not established.'
On p. 274 Schenk remarks with reference to the Cyanophyceae :
' Within the coloured zone (of the protoplast) lies the colourless
central body, which perhaps corresponds to a nucleus. How-
ever, the structure and division-figures characterising typical
nuclei have not been observed with any degree of certainty.'
F. G. Kohl on the other hand, in a recently published
work,1 declares with assurance that the central body in the
1 * t)ber die Organisation und die Physiologic der Cyanophyceenzelle und
die mitotische Teilung ihres Kerns ' (mit 10 Tafeln), Jena, 1903.
184 MODEEN BIOLOGY
Cyanophyceae is a true nucleus, and he proves such to be the
case from the processes of mitotic division that occur. Orville
P. Phillips l has come to the same conclusion, and thinks that
the Cyanophyceae can no longer be regarded as devoid of
nucleus.
The existence of true nuclei in Bacteria has lately been
asserted also by E. Eaymann and E. Kruis,2 and by F.
Vejdowsky.3
Even if we are obliged to regard the question of the
non-nucleate character of Bacteria and other diminutive
representatives of the lowest vegetable orders as to some
extent still doubtful, we can at least learn from the investi-
gations made on the subject, that the nuclear substance is
present in them, although it is broken up into little chromatin
granules or chromidia. They possess, therefore, what Wilson
calls a scattered or distributed nucleus (' The Cell,' p. 40),
and tKey^ ought not to be Considered simply non-nucleate,
although they seem to form a kind of transition to those
cells which contain a fully developed nucleus. That the
chromidia in Protozoa are the biological equivalents of nuclei
and only represent a particular condition of nuclear configura-
tion has been conclusively proved lately by Fritz Schaudinn.4
Oskar_Hertwig, one of the greatest biologists of the present
day, has declared it to be his opinion that really non-nucleated
organisms do not exist (' Allgemeine Biologie, 1906, pp. 44,
45). No actual facts can be brought forward in support
of them, only ' various theoretical considerations ' of a purely
speculative character ; as E. Hertwig expresses it (' Lehrbuch
der Zoologie,' 7th ed. p. 159) : ' It is easier to imagine that, in
spontaneous generation, those organisms first came into being
which consisted of only one kind of substance, than those
in which nucleus and protoplasm were already distinguished.'
1 ' Vergleichende Untersuchung der Cytologie und der Bewegungen der
Cyanophyceen ' (Contributions from the Botanical Laboratory, University of
Pennsylvania, II, ]904, pp. 237-306).
2 ' t)ber die Kerne der Bakterien ' (Bullet. International de VAcad. des
Sciences de Bohtme, VIII, 1903).
3 ' tiber den Kern der Bakterien und seine Teilung ' (Zentralblatt fur
Bakteriologie, XI, 1904, 2nd Part, pp. 481-496). Cf. the review in the Natur-
wissenschaftliche Rundschau, XTX, 1904, No. 29, pp. 366-369.
4 ' Neuere Forschungen iiber die Bef ruchtung bei den Protozoen ' ( Verhandl.
der Deutschen Zoolog. Gesellsch., 1905, pp. 16-25 and Plate I. See particularly
pp.,3-6).
NON-NUCLEATE CELLS 185
We cannot, therefore, name any independent unicellular
organism having either a cell-body without a nucleus, or a
nucleus without a cell-body. Is it possible that these forms,
so eagerly sought under Haeckel's name cytodes by the up-
holders of the theory of spontaneous generation, may occur
within the tissues of multicellular animals and plants ? If
they did occur, it would prove nothing in support of the
theory of spontaneous generation, for once-living cells can
degenerate and lose their nucleus, whilst cells still in
process of formation may have a nucleus before the layer of
protoplasm belonging to it can be traced.1 But in these cases
we should have to deal with the products of living, nucleated
cells ; not with a spontaneous coming into existence of non-
nucleated cell-bodies, or of bodiless nuclei, out of still
unorganised primitive matter. Let us examine the facts
rather more closely.
The young red blood-corpuscles of vertebrates have a
nucleus, which multiplies itself by direct division, and so
causes an increase in the number of red blood-corpuscles, as
we have already stated (Chapter V, pp. 86 and 87). The
old red blood-corpuscles lose their nuclei and become enucleate,
but they have ceased to be living cells, and are only the remains
of cells once alive, which still for a time are of use to the
organism as bearers of the oxygen loosely attached to their
haemoglobin, but soon they are dismissed from service, and
the white blood-corpuscles come and devour them. The exist-
ence of red blood-corpuscles without nuclei, accepted by most
authors,2 is of no use as evidence that there can be living
cells without a nucleus, and that the nucleus is not, therefore,
indispensable to the life of the cell. Just as a living cell
must have a nucleus or its equivalent, so a living nucleus must
have a protoplasm body, if it is to continue in existence. It
is true that there are cells in which the volume of the nucleus
is far greater than that of the cell body. Spermatozoa belong
to this class ; they often have an enormous head consisting
1 I observed instances of this when I was preparing the series of sections
of Lomechusa larvae. They occurred during the formation of new cenocytes
in the hypodermic region.
2 I say ' by most authors ' for some maintain that they have observed
nuclei even in old red blood-corpuscles. Cf. M. Duval, Precis d'Histologie,
pp. 50, 614, &c.
186 MODEKN BIOLOGY
of the nucleus of the sperm-cell, whilst the thin threadlike
tail and probably also the middle-piece, connecting it with the
head, are the protoplasmic elements of the cell ; but no sooner
has the spermatozoon lost its tail in the process of fertilisation,
than its existence as a cell is over ; its nucleus perishes, unless
it can unite with a female pronucleus to form the cleavage-
nucleus of the fertilised ovum (cf. Chapter VI, pp. 119, &c.).
We come now to the reverse case, in which new nuclei are
formed apparently without a cell-body. In the history of the
genesis of cells, these phenomena play an important part, as
we shall see later on. This is the so-called free nuclear
formation, which is supposed to lead to free cellular formation.
These formations were called free, because the new nuclei
were not formed by division from an old nucleus, nor the
new cells by division from an old cell, but both were supposed
to originate in an indifferent mass of protoplasm called blastem,
a product of the mother-cells in the same organism. Such a
mode of forming fresh nuclei, destined to become the centres
of fresh cells, even if it really existed, would have had
nothing to do with spontaneous generation, and it had no real
existence at all. The theory of free nuclear formation was, as
we shall see, to all intents and purposes dead at the end of the
nineteenth century, and in the twentieth no one can have
recourse to it to support any favourite theory.
Let us now sum up shortly the results of these investiga-
tions. They amount to this : There are no living organisms
simpler in organisation than the cell.
We can now approach the question : ' Is the cell the
ultimate unit of organic life, or is it composed of still lower
and more elementary units ? '
According to the laws of logic, we ought to describe as the
lowest unit of life only that part of a morphologically complex
living creature, which, at least under certain conditions, is
actually capable of an independent existence. Otherwise
it is no longer a biological unit, but only a part of a biological
unit. Now we have just shown that no organism is actually
of lower organisation than the cell, therefore the cell is actually
the lowest and ultimate unit in organic life.
We have seen moreover, in the previous sections, that
within the cell the nucleus and the protoplasm of the cell-
THE CELL AN INDIVISIBLE UNIT 187
body, as well as the morphologically distinguishable elements
of these two chief parts of the cell, are in no sense independent
of one another, but are closely connected, so as to make up
one cell, capable of life, to which they belong partly as essential,
partly as integral portions. The nucleus is in a certain degree
the material principle of organisation in the cell, controlling
its activities, but the protoplasm is indispensable to its life.
It is true that the chromosomes of the nucleus take the leading
part in the processes of cell- division, fertilisation, and trans-
mission of qualities, and possess some amount of individuality
(see pp. 167, &c.), as they always appear at the cell-divisions
in definite shape and number, and within these limits have an
independent power to propagate themselves and develop by
means of segmentation and growth ; but still no chromosome can
exist and become a nucleus without its corresponding particle of
protoplasm. And what does this show ? That the chromosomes
are not lower biological units within the cell, but they are
merely essential morphological and physiological constituents of
the cell. What is true of the chromosomes, applies also to
the centrosomes and to all the other less important morpho-
logical elements of the cell. None of them is capable of inde-
pendent existence apart from the cell ; they are, consequently,
only parts of the cell, not lower and more elementary units
out of which the cell is composed as a secondary formation.
The cell, therefore, from the biological point of view,
represents an indivisible unit, although it is composed morpho-
logically of many different parts, whose various functions
co-operate in the one biological process of life. The life of
a multicellular animal or plant is one biological whole, in
which the various organs, tissues, and cells, with their respective
functions, all unite and work together in conformity to law,
and the discovery of the intercellular bridges connecting the
various cells in the body of an animal or plant has furnished a
histological explanation of this fact,1 and in just the same
1 See Wilson, The Cell, 1902, pp. 59, 60. An excellent account of the
biological unity of the whole process of growth and development in the living
organism is given by the same author, pp. 58, 59, and 393, &c. According
to him (p. 59) cells are ' local centres of a formative power pervading the
growing mass as a whole.' 0. Hertwig too, in his Allgemeine Biologic, 1906,
chapter xiv, has done much to remove the obscurity prevailing on the subject of
' Individuality,' although I am unable to agree with him on all points, e.g.
in his conception of personality,' pp.JJ78 and 383.
188 MODERN BIOLOGY
way the life of a unicellular organism is an individual biological
unit, in spite of the fact that the cell is composed of various
parts with various functions. The impossibility of maintaining
the opinion that multicellular organisms are mere aggregations
of cells, has been brought out very clearly by 0. Whitman
in an article ' On the inadequacy of the cell-theory of develop-
ment ' (Wood's Hall Biological Lectures, 1893).
The cell-bridges forming protoplasmic connexions between
the cells of the organism may, according to Hammar,1 be
recognised even between the cleavage-globules of the first
divisions of the fertilised ovum. In his ' Allgemeine Biologie '
(1906, chap, xiv), Oskar Hertwig stoutly upholds the individual
unity of the multicellular organism. He distinguishes clearly
(p. 371) two different conceptions of individuality, viz. the
physiological and the morphological individual. The former
is ' an independent living being,' and it is to this alone that
the idea of individuality strictly speaking applies. The
latter is ' a formal unit, which resembles a physiological
individual morphologically, i.e. in appearance, structure, and
composition, but not in the physiological sense, for it is not
an independent living being, but is taken as a dependent
part into another higher physiological individuality, or, in
other words, is adopted as an anatomical element of the
same.'
The idea of organic individuality has in recent times often
been transferred from unicellular organisms to every single
cell of a multicellular organism, so that each cell in the body of
an animal or plant has been wrongly raised to the dignity
of an ' individual,' although it is not one at all physiologically,
i.e. it is not an independent individual, from the biological
point of view, but only a part of an individual.
In just the same way, in the lowest histological unit, viz.
in the morphological individual represented by the cell, the
part has often been confused with the whole, and attempts
have been made to prove, from the composition of the cell,
1 * t)ber eine allgemein vorkommende Protoplasmaverbindung zwischen
den Blastomeren ' (Archiv fur mikroskopische Anatomie, XLIX, 1897) ; ' 1st
die Verbindung zwischen den Blastomeren wirklich protoplasmatisch und
primar ? ' (ibid. LV, 1900). Cf. also Korschelt and Heider, Lehrbuch der
vergl. Entwicklungsgesch., Jena, 1902, Allgem. Teil, Part I, pp. 159, 160.
On the subject of intercellular bridges, see also 0. Hertwig, Allgemeinf
Biologie, pp. 400-406.
THE LOWEST VITAL UNITS 189
that there must be organic units of a lower order than the cell.
This line of argument is quite wrong, and we must clearly under-
stand that we may regard as the lowest units of organic life
only those parts of organisms which, at least under definite
conditions — such as occur among unicellular animals and
plants — are capable of independent existence. To call the
parts of these units ' subordinate units ' is most deceptive, for
they are not units at all, but only parts of units. All the
arguments adduced by Altmann, Schlater, and other modern
writers against regarding the cell as the final biological unit
are based upon this quibble. Flemming has shown this very
clearly with regard to Altmann, and says l that evidence is still
inadequate to prove that Altmann's granula are really ele-
mentary organic units or bioblasts, inasmuch as the chief point
in it is absent, viz. conclusive proof that one of his famous
granula is capable of exercising its elementary vital functions
outside the cell. We arrive therefore at the same result as
Oskar Hertwig in his ' Allgemeine Biologie ' (1906, p. 375), where
he declares cells to be the elementary units in the whole organic
world.2
If we wish to find a justification in fact for speaking of
' lower elementary units ' of living substance, we can do so
only in the sense in which Sachs spoke of energids. An energid
is a particle of nuclear substance with a definite amount of
protoplasm belonging to it and subject to its control. In this
way it would be possible to avoid the difficulties that seem to
prevent our giving the same account of cells with one nucleus
and of those with more than one. A cell with more than one
nucleus would be made up of a number of energids not so
completely distinct from one another as to be called separate
cells. A cell with one nucleus would be one fully developed
energid. The acceptance of this idea would obviously not
affect our opinion of the essential unity of the cell. We may
even imagine, as Lotsy does,3 that the first living beings were
monoenergids, i.e. very simply organised cells, consisting each of
a single energid. These might swim about freely, but we cannot
1 Cf. W. Flemming^ ' tJber Zellstrukturen ' (Naturwissenschaftliche Rund-
schau, XIV, 1899, No. 35, p. 444).
2 To understand his meaning more clearly, see also chapter xvii, pp. 424,
&c., of the same work.
3 Biolog. Zeniralblatt, 1905, No. 4, p. 97.
190 MODEEN BIOLOGY
possibly imagine biophors or other ' lower elementary units '
to have swum about, because they, as far as they have any real
existence, are only parts of an energid, and not creatures capable
of independent life.
Thus we arrive again at the conclusion : The cell (or
energid) is actually the lowest unit in organic life. Therefore
the alleged ' lower elementary units ' of the upholders of the
Theory of Descent are nothing but fictions. It is a matter
of complete indifference for this subject whether the formations
in question can be seen under the microscope, as definite
morphological elements of the cell, or whether they exist
solely as figments of the imagination in the brain of some
philosophising naturalist, for their interpretation as elementary
units is in both cases equally imaginary, although they may
retain their significance as more or less hypothetical elementary
parts of the living substance.
I should stray too far were I to attempt to give my readers
anything like a complete account of the many various theories
in which these elementary units are concerned. The names
given to these units by those who believed they had discovered
them are very numerous. In 1864 Herbert Spencer began
the list by calling them physiological units ; Darwin called them
gemmules, Erlsberg and Ernst Haeckel plastidules, Nageli
micellae, Detmer Lebenseinheiten or vital units, Hugo de Vries
pangens, Verworn biogens, and Weismann biophors, which by
combining make up the units next above them or determinants,
which in their turn compose ids and ids idants. (Cf . Chapter VI,
pp. 107, &c. and pp. 175, &c.) W. Koux called his elementary
units metastructural parts, Wiesner plasomes, W. Haacke
gemmae, which he imagines as rhomboid crystals lying side by
side to form magnetic columns or gemmaria.1
L. Zehnder2 conceives of the elementary units of life as
annular hollow cylinders, formed of organic molecules, and
he calls them fistellae. Oskar Hertwig calls his units bioblasts,*
1 For a criticism of Haacke's fantastic ' Doctrine of Creation,' see my
article, ' Zur neueren Geschichte der Entwicklungslehre in Deutschland : Eine
Antwort auf W. Haacke's Schopfung des Menschen,' Miinster, 1896 (Natur und
Offenbarung, XLII).
2 Die Entstehung des Lebens aus mechanischen Grundlagen entwickelt, I,
Freiburg i. B., 1899, pp. 50-52.
3 Allgemeine Biologie, 1906, pp. 52, &c.
THE LOWEST VITAL UNITS 191
Simroth : biocrystals, and Altmann granula, bioblasts or auto
blasts — granula, inasmuch as they are visible under the micro-
scope as very fine grains ; bioblasts, inasmuch as they re-
present the hypothetical elementary units of the life of the cell ;
and autoblasts, inasmuch as they are said to be capable of a
free existence outside the cell. It is a pity that neither Altmann
himself nor any of his followers, among whom Gustav Schlater
is conspicuous for his energy,2 have succeeded in demonstrating
the existence of granula as bioblasts and autoblasts.
1 am far from denying that the above-mentioned theories
contain many ideas that are both accurate and fruitful for the
philosophy of life. (Cf. 0. Hertwig, ' Allgemeine Biologie,'
chapter xxxi.)
Kichard Hertwig has drawn attention3 to the fact that
according to most recent research, the chromatin of the cell-
nucleus really possesses the properties which Nageli required
theoretically for his idioplasm as the material substance of
heredity (1884). This hypothetical substance in the first place
must not only be organised at the time of fertilisation, but it
must have possessed its organisation beforehand, and have
constantly preserved it ; secondly, it must be present in the
egg- and sperm- cell in equal quantities ; and thirdly, it must
occur in all cells in a state of living metamorphosis, and influence
their vital processes. The chromosomes of the nucleus possess
all these properties, as I have shown plainly in my account of
the processes of cell division and fertilisation (Chapter V,
pp. 123, &c. and pp. 165, &c.). That the chromatin of the cell-
nucleus is a real idioplasm, a real physical basis of inheritance,
we must acknowledge to be extremely probable ; but, on the
other hand, it is wrong to follow Nageli in regarding the single
particles of chromatin, micellae, as he calls them, as elementary
vital units ; for, from their very nature, the chromosomes can
only be parts of the nucleus of a living cell, with which the
substance of inheritance is necessarily connected. A living
* Bemerkungen zu einer Theorie des Lebens ' ( Verhdndl. der Deutschen
Zoolog. Gesellsch, 1905, pp. 214-232).
2 Cf. his articles : ' Der gegenwartige Stand der Zellenlehre ' (Biolog.
Zentralblatt, XIX, 1899, Nos. 20-24); ' Monoblasta— Polyblasta— Poly-
cellularia ' (ibid. XX, 1900, No. 15).
3 ' tJber Befruchtung und Konjugation (Verhandl. der Deutschen Zoolog.
Qesellsch., 1892, p. 101).
192 MODEEN BIOLOGY
chromosome apart from a corresponding particle of living
protoplasm is an impossibility.
I will gladly acknowledge that many of these theories
of heredity display a marvellous wealth of ingenuity and
intellectual effort. This is particularly true of Weismann's
Germ-plasm theory, especially in the form of the Theory of
Determinants, in which he stated it in his lectures on
the Evolution Theory in 1892. It aims at explaining the
nature of the germ-plasm, and of all the phenomena of
heredity, by reference to particular structures and par-
ticular distribution of even the smallest material parts of the
germ-plasm. As a general theory, however, it proves to be
untenable.1
It seeks in a one-sided way to account for the development
of the individual out of the preformed structure of most
minute material particles of germ, and finally it is reduced to
the necessity of assuming the existence of ' vital affinities '
between these minute particles, and this necessity reveals the
inadequacy of the ingeniously thought-out mosaic theory.
I should prefer to accept Oskar Hertwig's Theory of Biogenesis
(' Allgemeine Biologie,' chap.xxii, &c., and especially pp. 635,
&c.) which, in a successful and logical manner, connects the prin-
ciple of preformation with that of epigenesis. It too regards
the chromosomes as the material bearers of heredity, but takes
into account also the dynamic and physiological force of their
interaction in the vital unity of the whole process of develop-
ment. If we therefore consider 0. Hertwig's hypothetical
bioblasts to be elementary particles, and not elementary units
of living substance, the theory of biogenesis, as a working
hypothesis, is of assistance to us in trying to solve the problem
of evolution. 0. Hertwig himself frequently emphasises the
facts that a cell containing a nucleus is the lowest morpho-
logical unit in organic life, and that the cells in multicellular
organisms unite to form a true, physiological, living unit. On
p. 569 he sums up his opinion as to the causes of development
as follows : ' Continuity in development is not attained by
means of the emboitement of miniature creatures, nor by the
1 For a criticism of it, see Y. Delage, La structure du protoplasma et Us
theories fur Vheredite, pp. 196, &c., 512, &c., 667, &c. ; also J. Keinke, Philosophic
der Botanik, 1905, pp. 63, 64. 0. Hertwig, op. cit., 1906, pp. 361, 452, &c., 620,
633, &c. Cf. also Chapter VI, pp. 174, &c.
SPONTANEOUS GENERATION 193
secretion of an unorganised formative material endowed with a
nisus formativus, nor by a substance composed of tiny germs,
and so to some extent representing an extract of the body,
but rather by the cell, a living elementary organism, which
by its multiplication and combinations gives rise to all forms
of vegetable and animal life. Continuity of organic develop-
ment and of organic life depends therefore on the principle
omnis cellula ex cellula.'
Zoological and botanical research, whilst it has enlarged our
knowledge, has tended more and more to prove the non-exist-
ence, among unicellular organisms, of any that really consists
of a simple lump of plasm, such as the theorists are so anxious
to discover. Fritz Schaudinn, who is one of our best authori-
ties on Protozoa, gave an address on ' Recent Research into
Fertilisation among Protozoa ' (' Neuere Forschungen iiber
die Befruchtung bei Protozoen ') at a meeting of the German
Zoological Society at Breslau, on June 14, 1905, and the
opinion, which he expressed in the following resigned terms,
must be valuable. He said : ' As in the class of Flagellata,
universally regarded as one of the lowest groups of Protozoa, the
study of the problem of fertilisation alone shows the finer
structures of the cell to be almost as highly differentiated and
complicated as in the highest organisms, the discovery among
Protozoa of our day of that tiny drop of simple plasm, whence
the animal cell is supposed to have originated, may present
some difficulties.'
2. SPONTANEOUS GENERATION OF ORGANISMS
The question as to the lowest actual units of organic life
is closely connected with the question whether spontaneous
generation is possible.
The Monists assure us that it is undoubtedly possible,
because it must have taken place ; organic life exists now in the
world, and yet there was a time when it did not exist, as the
world was still in a state of molten heat. Therefore there must
have been an epoch when, under particularly favourable
chemico-physical conditions, the first primordial plasm or
plasms were produced from inorganic combinations of carbon.
The assumption of spontaneous generation is therefore an
194 MODEKN BIOLOGY
indispensable postulate of science, according to Monism. M.
Verworn, the eminent physiologist,1 argues in the following
way in favour of spontaneous generation : ' Living substance is
actually a part of the matter composing our world. The com-
bination of this matter to form a living substance was as much
a necessary result of the evolution of the world as the formation
of water, viz. a necessary result of the gradual cooling of
those masses which made up the crust of the earth. In
the same way the chemical, physical, and morphological
properties of living substance, as we know it, are the
inevitable consequence of the working of our present ex-
terior conditions of life upon the interior conditions of earlier
living substance. Interior and exterior conditions of life
stand in inseparable interaction, and the expression of it
is life.' Thus the assumption of spontaneous generation is
scientifically irrefutable !
What are we to say in answer to this demand made upon
us in the name of science ? I am quite ready to admit that the
first organisms were made of inorganic matter, for, if they
were not, they would have to be created out of nothing, which
I am by no means inclined to believe. But the theory _of
spontaiieousgeneration requires inorganic matter to., have
first organisms by itself and ont. pf its own
resources. Thelatter assumption cannot be a ' postulate
oT science,' because, as I shall show, it plainly contradicts
actual facts. If I were to maintain, on the contrary, that the
first living beings were brought forth from matter still not
organised,2 under the action of a higher power proceeding from
the Creator of matter, I should have given up the idea of
spontaneous generation, and have replaced it by that of
creation in the wider sense. I say ' creation in the wider
sense,' because the matter out of which the organisms were
formed already existed, and the creative action was limited
to the organisation of this matter. It is quite indifferent to
our question how we imagine this organisation to have taken
place, whether it was by an eductio formarum e potentia
1 Allgemeine Physiologic, 1901, pp. 333, &c.
2 The antithesis is between organised and not organised, not between
organic and inorganic, for many organic substances, i.e. such as under natural
conditions are formed only in living organisms, can be made artificially in
chemical laboratories.
SPONTANEOUS GENEKATION 195
materiae, or by some other method ; nor do we know when the
first organisation of matter occurred.1
It is obvious that the material basis for the origin of the
first forms of life must be supplied by definite arrangements of
atoms and the physical and chemical laws governing them ;
but this no more proves spontaneous generation to have taken
place than does the fact that also at the present time the
phenomena of life rest on a chemico-physical foundation.
The problem with which we are now concerned is therefore
the following : ' What are we to think of the theory of spon-
taneous generation, which requires lifeless matter of itself
to have produced the • first living organisms ? ' We must
examine the scientific character of this spontaneous generation
more closely.2 We may disregard those rash and untenable
theories which, like Ernst Haeckel's carbon theory, aim at
giving a direct account of spontaneous generation. It is im-
possible not to be amazed at the audacity with which these
hypotheses are published as being the results of scientific
research. For instance, in 1892, S^haafflaussn seriously
asserted that water, air, and various mineral substances had
united directly under the influence of light and heat, and had
produced a colourless Protococcus, which afterwards turned
into the Protococcus viridis. Yves Delage remarks somewhat
sarcastically : 8 'If the matter is so simple, why does not the
author produce a few specimens of this protococcus in his
laboratory ? We 'would gladly supply him with the necessary
chlorophyll.' Still more fantastic is Haeckel's discovery
1 Hamann (Darwinismus und EntwicJclungslehre, 1892, p. 58) and Fechner
assume that matter was originally in a ' cosmo-organic ' state, subject to the
laws of neither organic nor inorganic nature, but this hardly seems to be a
tenable hypothesis, for the chemico-physical laws governing the atoms and
molecules in matter can scarcely have differed from those that now govern
inorganic matter, and, in the same way, the mechanical laws governing the
movement of atoms, molecules, and masses must have been identical with the
present laws. It follows that primitive matter in itself must be judged accord-
ing to the laws of the present inorganic world, and so the ability to produce
organisms spontaneously cannot have belonged to its essence.
2 On the differences between living creatures and lifeless matter
see also L. Dressel, Der belebte und der uribelebte Rtoff, Freiburg i. B., 1883.
I cannot here discuss the other reasons for declaring the theory to be
philosophically untenable. Stolzle remarks very justly (A. v. Kolliker's
6 Stellung zur Deszendenzlehre,' 1901, p. 14) that as an explanation the theory
of spontaneous generation is worthless, if for no other reason, because it
attempts to explain the unknown, not by the known, but by another unknown.
3 La structure du protoplasma et les theories sur rherediie, p. 402.
o 2
196 MODEKN BIOLOGY
of an organic primitive pulp to which he gave the classical
name of Autoplasson, or self-forming substance. We have
already seen how badly Bathybius Haeckelii has fared, which
was supposed to be the first real representative of this pulp.
On a level with Haeckel's autoplasson is the plastic primary
substance discovered in 1874 by an Italian named Maggi, who
called it Gliq, and declared it to be the starting-point of the
development of the organic world. It does not altogether
savour of genuine science.
Thoughtful naturalists cannot regard as serious such
clumsy attempts to solve the most delicate problems ; it is
obvious that they are doomed to be failures. The chemical
composition of nucleinic acid,1 which is present chiefly
in the chromatin (nuclein) of the nucleus, and is therefore
intimately connected with the problem of heredity, defies
all the attempts made hitherto, and likely to be made in future,
by the upholders of the carbon theory to explain its chemical
formula C26H49N9P3022. That it is a hopeless task to seek
the origin of life directly from inorganic matter is acknow-
ledged frankly by most naturalists. If theories, such as
Haeckel's carbon theory, are still brought forward, it is not for
the benefit of really scientific circles, but that the so-called
' general ' readers may be disposed thereby to accept a realistic
and monistic view of life.
I have, of course, no intention of condemning the ingenious
attempts, which chemists are making with ever-increasing
success, to produce organic matter artificially in their labora-
tories. By means of unwearied industry, Emil Fischer and
other eminent workers in this department of research have
advanced steadily towards mastering the chemical construc-
tion of a molecule of albumen,3 and, perhaps, erelong the
1 For a detailed account of the chemistry of the nucleus see Dr. Hans
Malfatti, Zur Chemie des Zellkerns : reprinted from the Berichte des natur-
wissenschaftlich-medizin. Vereins in Innsbruck (XXII, 1891-2). Cf. also
Hof meister, ' "Dber den Bau des Eiweissmolekiils ' ( Verhandl. der 74 Versamm-
lung Deutscher Naturforscher zu Karlsbad, 1902, communicated to the Natur-
wissenschaftliche Rundschau, 1902, No. 42). Also Wilson, The Cell, pp. 41,
330, &c. ; 0. Hertwig, Allgemeine Biologie, 1906, pp. 29, &o.
2 Cf. Karl Kautzsch, ' Uber das Eiweiss, insbesondere die neuesten For-
schungen auf dem Gebiete der Eiweisschemie ' (Natur und Schule, V, 1905,
pp. 195-208) ; G. v. Bunge, Lehrbuch der Physiologic des Menschen, II, 1905,
pp. 55-70 ; Fr. Samuely, ' Die neueren Forschungen auf dem Gebiete der
Eiweisschemie und ihre Bedeutung fur die Physiologic' (Biolog. Zentralblatt,
1906, Nos. 11, 12, 13-15) ; 0. Hertwig, Allgemeine Biologie, chapters ii, iii.
SPONTANEOUS GENEKATION 197
artificial synthesis of the simplest forms of albumen will be
accomplished by these indefatigable students. But this would
prove nothing about spontaneous generation. The albumen
molecules, with their highly complicated chemical composition,
are the constituents of living creatures, but even in the smallest
cell these constituents are alive, and no astute human in-
telligence will ever succeed in breathing the breath of life,
capacity for growth and propagation, into one of these arti-
ficially prepared, lifeless molecules of albumen, and still less
can chance ever have been in a position to form molecules of
albumen by itself. Oskar Hertwig remarks very aptly in his
' Allgemeine Biologie ' (1906, p. 19) : * Even if chemistry in
course of time were able to produce artificially by synthesis
all existing forms of albumen — to undertake to form a proto-
plasmic body would still resemble Wagner's attempt to
crystallise out_a_homunculus in ajtest-tube.'
Modern physics will in vain strive to do what organic
chemistry fails to accomplish. It is not long since people
believed that the discovery of radium had removed the hindrance
which had frustrated all previous attempts to produce life.1
On June 30, 1905, John Butler Burke, of the Cavendish
Laboratory in Cambridge, startled the scientific world by
announcing that, with the help of radium, he had succeeded
in producing from sterilised bouillon a substance that showed
certain signs of life : the first living albumen body appeared
to have been born artificially ! But it was unhappily a mis-
carriage. Sir William Eamsay, the famous physicist and
investigator of the properties of radium, soon explained what
Burke had observed, and accounted for it in a very simple
way. The powdered radium, which Burke had strewn upon
the bouillon, produced in it chemical changes. The emanation
of the radium decomposes the water in the bouillon into
oxygen and hydrogen, and has at the same time the peculiarity
of coagulating albumen. Consequently this emanation could
not fail to form, in any watery fluid containing albumen,
little bubbles of gas surrounded by a covering of coagulated
albumen. As more gas is produced, these bubbles increase
and occupy more space, so as to present the appearance of a
very small, growing organism. In reality, therefore, this
1 ' Das Radium und die Urzeugung ' (Oaea, XLII, 1906, Part I, pp. 34-36).
198 MODEEN BIOLOGY
alleged living creature was nothing but a lifeless covering of
albumen filled with gas ! This explains a phenomenon observed
by Burke, viz. that the new-born organism melted away in
the water, for the water gradually removed the gelatine from
the ' cell- walls,' and they returned to lifeless non-existence.
We cannot waste time here on the refutation of the various
old and new theories of spontaneous generation ; we will
rather turn our attention to the attempts made by scientific
men to present the problem of spontaneous generation in a
1 more comprehensible or more acceptable ' form. To this
category belong the theories that have devised the simplest
possible elementary units of life, in order by their means to
bridge over the chasm between the atoms and molecules of the
inorganic world and the simplest forms of life ; or, if the chasm
cannot be actually bridged, they aim at diminishing its width
to such an extent that a bold ' stroke of genius ' may help
them over it. To leap from inorganic matter, or even from
artificially produced organic combinations, to the living cell
is a very hazardous proceeding, which even the most daring
advocate of the theory of evolution would hesitate to venture
upon. Therefore there is only one way of getting over the
difficulty. The chasm must be crossed, not at One bound,
but by degrees, and so intermediate halting-places are neces-
sary. These hypothetical intermediate stations are called
' simpler elementary units of life ' ; they are used to make up
the phylogeny of the cell by means of the assertion that nature
has taken these steps before us, in order to produce the first
cell out of inorganic matter. In this way the theory of spon-
taneous generation is supposed to be made more acceptable
from the scientific point of view.
The statement just given is not an invention of my own,
it is only a short summary of the way in which Gustav Schlater
in the Biologisches Zentralblatt for 1899 (pp. 729, &c.) tries to
give a phylogenetic value to Altmann's granular theory.
Schlater thinks that Altmann's newly discovered elementary
units are of great importance, chiefly because they bring us
nearer to a comprehension of spontaneous generation. He
says on this subject (p. 732) : ' Although at the present time
we are naturally not yet in a position to fix the moment when,
through a complicated molecule of albumen, the first ray of
SPONTANEOUS GENERATION 199
life flashed, which changed the dead molecule into a living
organism, or, let us say, into an autoblast ; nevertheless such
a change is much more within our comprehension than such
a gigantic transition in evolution, as that from a dead molecule
of albumen to a complicated organism like the cell.'
There must have been a flash somewhere for life to have
begun at all ; even Schlater acknowledges this. But it is
eventually a matter of perfect indifference whether the flash
was at the spontaneous generation of an autoblast or of a cell ;
the flash of the first spark of life in lifeless matter is as in-
explicable in the one case as in the other. Schlater might have
saved himself the trouble of writing over a hundred pages in
support of bioblasts and autoblasts, for by so doing he has
quite gratuitously brought himself into conflict with scientific
facts, which know nothing of autoblasts, i.e. of Altmann's
granules with a free and independent existence, but recognise
cells as the lowest units of organic life. He has brought himself
needlessly into conflict with scientific laws of thought, which
forbid us to regard Altmann's granules as bioblasts, i.e. as real
elementary units of life, because they are actually only biologi-
cally dependent parts of the real biological units, viz. the cells.
So Schlater's whole argument misses its point. He has not
succeeded in establishing the existence of elementary units,
having a lower degree of organisation than the cell ; nor has
he succeeded in explaining the origin of life, even by assuming
the existence of these units. The summa summarum is in
his case another unmistakable breakdown of the theory of
spontaneous generation.
Therefore in 1899 the theory did not fare better than in
the previous contests that it had had to undergo. It has always
suffered defeat, and as scientific research advances, it with-
draws into obscurity. It may, perhaps, be interesting to give
my readers a short sketch in broad outlines of this retreat of
the theory of spontaneous generation.
There was a time when generatio aequivoca or spontanea
was regarded not only as possible, but as of actual occurrence.
This was during the so-called ' dark ages ' and the still
darker mediaeval period. At that time men believed that
the origin of organic beings was influenced to a great extent
by the stars. I am not referring to the dreams of astrologers,
'200 MODERN BIOLOGY
but to the Aristotelian theory of the formation of new organic
beings from decaying substances, the cause of which was
supposed to be a mysterious power proceeding from the
heavenly bodies. This ancient theory of spontaneous genera-
tion is far less contrary to common sense than the modern
theory, and considering the state of scientific knowledge at
the time was far more pardonable. It was taken up in very
various ways by the naturalists, poets, and quacks of the period.
As an example I may refer to Vergil's ' Georgics,' where there
is a^recipejor making bees. A dead ox is to be laid out, beaten
vigorously, and left to decompose in its hide, until the bees
develop in its body. Vergil did not draw upon his imagination
when he gave this recipe ; it is based upon real observations
wrongly interpreted. There are some robber flies that
resemble bees very closely, belonging to the genus Eristalis,
the larvae of which develop in decomposing matter. It might
easily escape the notice of a casual observer that the old flies
had already laid their eggs there. Even the famous ant-stone,
lapis myrmecias, which was supposed to grow in ants' nests
and to combine the nature of the ant with that of a precious
jewel, able to cure various ailments among mankind, is no
mere fiction. The story originated in the discovery in ants'
nests of the cocoons of the rose chafer (Cetonia floricola) which,
when the beetle has developed, really contain a living jewel
of a golden or emerald green colour, in a covering of the size
of a pigeon's egg, formed of earth.1
As methods of observation improved in modern times,
the theory of spontaneous generation gradually lost favour.
As early as the seventeenth and eighteenth centuries it was
challenged by naturalists, such as Eedi, Malpighi, Swammerdam
and Reaumur, and was pushed into the background, although
in the nineteenth century it had some champions who defended
it theoretically. In the middle of the nineteenth century
much was done to overthrow it by von Siebold and E. Leuckart
in the department of parasites, by Ehrenberg in that of In-
fusoria, and by de Bary, and especially by Pasteur in that of
Bacteria. Thus modern scientific research has removed one
support after another from the theory of spontaneous genera-
1 Of. Lochner v. Hummelstein, ' Lapis myrmecias falsus, cantharidibus
gravidus ' (Ephem. Ac. Nat. Curios, 1687, Observ. ccxv, 436-441).
OMNE VIVUM EX VIVO 201
tion, until now nothing is left of it — except that it is 'a postulate
of science.'
As early as 1651 an Englishman/17 William Harvey,
formulated the famous principle Omne vivum ex ovo, in his
work ' De generatione animalium.' In this form the dictum
is not universally true, for the unicellular organisms multiply
themselves not hy eggs, but by cell-division or gemmation,
which is, however, only a special form of cell- division (see
p. 86). Therefore Harvey's saying must be amended and
receive the form : Omne vivum ex vivo. It was not until two
hundred years later that Rudolf Virchow, the founder of cellular
pathology, in 1858 set the modern axiom of biology, Omnis
cellula ex cellula, beside Harvey's dictum.
The theory of spontaneous generation found for a time
its last refuge in just that cellular theory which subsequently
dealt it its death-blow. In order to account for the origin
of the cell, Schwann propounded his Cj/toUa^tema theory,
according to which cell-formation took place by way of a sort
of crystallising process in matter still unorganised. The first
deposit from the primitive matter or cytoblastema was,
according to Schwann, the nucleolus of the cell, round which
a membrane formed ; between the nucleolus and the membrane
a fluid penetrated by endosmosis, so forming the cell-nucleus ;
round this again there was a second membrane, and by endos-
mosis more fluid made its way between this membrane and
the nucleus, so that finally the membrane enclosed the cell,
having in its centre the nucleus with the nucleolus.
Schwann imagined the cell to have been formed in this way
spontaneously out of unorganised matter by generatio
aequivoca. It was a most ingenious idea, but it did not
correspond with facts, and it soon had to be given up.
The somewhat later blastem theory advanced by Charles
Eobin, a French scientist, has this advantage over Schwann's
cytoblastema theory, that it does not assume the formation of
cells out of unorganised matter. Kobin's blastems, which
give rise to new cells, are the product of previously existing
cells of the same organism. It is, therefore, not correct here
to speak of a generatio aequivoca. Kobin's theory was nearer,
to the process that really goes on in cell-formation in another
respect also, for he thought that the nucleus of the new cell
202 MODERN BIOLOGY
was formed before the nucleolus. Bound the nucleus a layer
of protoplasm took up its position and finally surrounded
itself with a membrane. This account of the genesis of the
cell also failed to agree with ascertained facts. It is true that
for a considerable time it found much support in the embryonic
development of insects. Hugo von Mohl had proved that
free cell-formation did not occur among plants, and Albert von
Kolliker had proved its non-occurrence among animals ; it
had long been established that among higher animals the blasto-
derm of the embryo had its origin in continued cell-division
from the cleavage-nucleus produced by the union of the egg-
and sperm-nuclei, and yet for some time it seemed that among
insects there was free cell-formation in Robin's sense. In
1864, in his classical studies on the development of Diptera,
August Weismann still felt bound to uphold this theory of
free cell-formation, as he could not perceive any processes of
cell- division in the formation of the blastoderm in these
insects. As recently as 1888 Henking l thought that he had
found that the nuclei of the blastoderm in the egg of Musca
were not formed by division from the cleavage-nucleus, but
by free nuclear formation in the isolated particles of plasm
dispersed among the masses of yolk.
On this subject Korschelt and Heider remark in their
excellent ' Lehrbuch der vergleichenden Entwicklungsgeschichte
der wirbellosen Tiere' (special section, part 2, Jena, 1892, p.
764), that this opinion seems to be quite untenable. In those
insect eggs which are so extraordinarily rich in nutritive yolk
(deuteroplasm) as are the eggs of flies, the processes of cell-
division are very apt to escape observation under the micro-
scope. In other insect eggs that contain less yolk (such as
those of the plant-louse, gall-gnat and gall-fly), these processes
have undoubtedly been observed, and we must take the
latter, rather than the former, as illustrating the normal
course of blastoderm formation in the eggs of insects. Thus
the last support of free cellular formation has been removed,
and we now have a general law that, not only does every new
cell arise out of a previously existing cell, but each new nucleus
out of a previously existing nucleus.
* Die ersten Entwicklungsvorgange im Fliegenei und freie Kernbildung '
(Zeitschrift fur wissenschajtliche Zoologie, XLVI).
OKIGIN OF LIFE 203
Walter Flemming in 1882 added the third dictum, Omnis
nucleus ex nucleo, to the two biological axioms laid down by
Harvey and Virchow respectively. As Boveri's theory of
the individuality of the chromosomes (see p. 167) is constantly
receiving fresh confirmation, we must add yet a fourth dictum,
dating from 1903, viz. : Omne chromosoma e cJiromosomate.
In it the antagonism shown by modern biology to the theory
of spontaneous generation has reached its climax. The four
axioms — Omne vivum ex vivo, Omnis cellula ex cellula,
Omnis nucleus ex nucleo, Omne chromosoma e chromosomate —
have destroyed the theory as far as modern naturalists are
concerned. It can continue to exist only outside the sphere
of scientific thought.
Very descriptive of the scientific weakness of the theory
of spontaneous generation are the following remarks which
occur in the famous biologist, Oskar Hertwig's ' Allgemeine
Biologie ' (1906, p. 263) : ' Considering the state of natural
science at this time, there seems but little prospect that any one
engaged in scientific research will succeed in artificially pro-
ducing even the simplest living organism from lifeless material.
He has certainly no more hope of success than Wagner in Goethe's
" Faust " had in his attempts to brew a homunculus in a retort.'
J. Eeinke, the distinguished botanist, has expressed
himself much more sharply still on the subject of the theory
of spontaneous generation, in many places in his works.1
It is, therefore, an absolutely necessary consequence that
organic life on earth did not begin by way of spontaneous
generation, and that it is altogether unscientific to represent
this theory as a postulate of science, in spite of its being quite
untenable. Our modern evolutionists above all others lay
great stress upon the fact that the laws of nature now existing
1 See his book Die Welt ah Tat (Berlin, 1899), the third edition of which
appeared in 1903. In it J. Keinke devotes a chapter, almost thirty pages
in length, to proving the impossibility of spontaneous generation, and he
deduces from this argument the conclusion that we shall_neyer be able IP
account for the origin of organic life unless we accept the creation^ In 1905
a fourth edition was published] Ci also J. .kemke's Einleitung in die theo-
retische Biologie, 1901, pp. 555-562, and his treatise ' Der Ursprung des Lebens
auf der Erde ' (Turmer Jahrbuch 1903) ; also his inaugural oration at the
International Botanical Congress in Vienna, June 12, 1905, ' Hypothesen,
Voraus^etzungen, Probleme in der Biologie ' (Biolog. Zentralblatt, XXV, 1905,
No. 13, pp. 433-446), pp. 442, 443. He has an excellent refutation of the
hypothesis of spontaneous generation in his last book, Philosophie der Botanik
(Leipzig, 1905), chapter xii, On the Origin of Life.
204 MODEBN BIOLOGY
must have existed from the beginning, and that we must
regard them as a safe standard, applicable also to the most
remote history of the animal and vegetable world, if we wish
to solve the problem of descent scientifically. It is quite in
vain that they appeal to the * uniform causal connexion of
natural phenomena ' to support the theory of spontaneous
generation. J. Reinke says very aptly (' Einleitung in die
theoretische Biologie,' p. 558) : ' I am of opinion . . . that
the assumption of spontaneous generation in past ages agreed
no more with our ideas of causality than a hypothesis that a
million years ago water flowed uphill of its own accord would
agree with them.' And in another place he says (' Philosophic
der Botanik,' p. 188) : ' Just as at no stage of the earth's
cooling was it possible for two lines to form a triangle, so was
it never possible for an organism of the most primitive kind
to be produced by the forces and combinations of inorganic
matter.' There is therefore, as Reinke rightly points out,
scarcely a greater incongruity possible, than for one and the
same man to reject spontaneous generation, as a thoughtful
naturalist, and in the same breath to declare it to be a postulate
of science, when he speaks as a philosophical thinker. What
is a ' postulate of science ? ' This name can properly be
given only to a truth that proceeds logically from facts, and
never to a hypothesis that is in antagonism to them.
From this point of view, what true postulate of science is
there to account for the first origin of organic life ?
Life cannot always have existed on our earth ; modern
cosmogony leaves us no room to doubt this, for it teaches
us that the earth was once in a condition of molten heat.
How, then, did the first organisms come into being ?
It is an unprofitable amusement to fancy, with Thomson
and Helmholtz, that they were brought by meteors from other
planets, or, with H. E. Richter and Arrhenius, that they fell
upon the earth as cosmic dust,1 for life must have had a beginning
1 In his Einleitung in die theoretische Biologie, p. 559, Reinke says : ' Men
like Lord Kelvin (Thomson) and Helmholtz would not have devised their
hypothesis of the advent of primitive cells from other planets, if they had
not regarded spontaneous generation as lost beyond all hope of recovery.'
It should be noticed that Thomson has repeatedly and decidedly said that
we must assume the existence of a Creator. Cf. Karl Kneller, S.J., Das
Christentum und die Vertreter der neueren Naturwissenschaft, Freiburg i. B.,
1903, pp. 28-30, and The American Quarterly Review, XXVIII, 1903, p. 603.
THEOKY OF CKEATION 205
on the planets of other solar sj^stems also, since they too
are subject to the same cosmogonic laws.
Therefore, how did the first organisms come into being ?
Every effect must have an adequate cause. Inorganic matter
cannot have been this cause, for science teaches us this when
she declares spontaneous generation to be contradictory to
facts. But at that time there was still nothing in the world
but inorganic matter and its laws. Therefore there must
have been some cause extraneous to this world, which brought
forth the first organisms out of matter. This cause, extraneous
to the world, and differing substantially from it, in spite of its
omnipresence in it, is an intelligent cause, and is the personal
Creator, so often denied and feared by modern monism.
Monism, in its desire to get rid more easily of the theistic
conception of God, has caricatured it, until finally the Creator
has been represented as a ' gaseous vertebrate ' (Haeckel),
bearing alarming testimony to its discoverer's want of philo-
sophical knowledge. The new idea of God invented by monism,
and set up in place of the personal Creator, is nothing but a
fantastic sort of idol draped in a covering of theism to hide its
atheistic nakedness. Everything acceptable in the monistic
idea is borrowed from theism, the omnipresence of God in
nature, His action in all creation, &c. But what is peculiar
to monism, and marks it off from theism, is the theory of the
substantial identity of God and the world, which is nonsense
from the philosophical point of view. A god identical with
the world, and developing himself through TtTisTnot an infinitely
perfect being, having the reason of_hia_£xistence always in
himself, but he is a mass of imperfections and contradictions .
Any thoughtful student of nature must be able to see this
for himself.
We may therefore close our examination of the theory
of spontaneous generation with the following statement :
Organic life has not always existed in our world, nor can it
have originated by itself from inorganic matter. Natural
science brings us thus far ; and natural philosophy leads us
on to the further irrefutable conclusion : — It follows that
some cause superior to the world produced the first organisms
from lifeless matter. When and how this took place is perfectly
indifferent, as far as the necessity of this conclusion is concerned.
206 MODEEN BIOLOGY
Even if we did not need to assume the existence of any special
vital principle, and if the living atoms differed from inorganic
matter only by being in a state of movement peculiar to them-
selves, we could still not dispense with the Creator to create
primitive matter, and to impart to those atoms their state of
movement, in order thereby to make them the constituents of
the first living creatures. But we are still more forcibly
constrained to acknowledge the existence of a personal Creator
by the fact that modern science proves, more and more clearly,
that all vital processes are subject to their own particular law,
and we are thus compelled to accept the entelechies, or formal
principles, which raise the laws governing inorganic matter
to a higher, vital conformity to law in the case of living
creatures.
Thus the acceptance of a personal Creator is seen to be a
real ' postulate of science.' For, as J. Keinke rightly points
out : ' If we assume at all that living creatures once were
formed of inorganic matter, as far as I can see, the theory of
creation is the only one which satisfies the demands of logic and
causality, and so satisfies those of reasonable scientific research.'1
1 Einleitung in die theoretische Biologie, p. 559. See also the quotations from
Charles Darwin and Lyell on the indispensability of a creation in Chapter IX,
at the end of § 6.
CHAPTEK VIII
THE PROBLEM OF LIFE
INTRODUCTION AND SURVEY or THE VARIOUS TYPES OF CLEAVAGE.
1. THE PROBLEM OF DETERMINATION AND ITS HISTORY.
Mechanics and physiology of development (p. 211). History of the
theories of preformation and epigenesis (p. 214). Germ-regions for
the formation of organs and isotropy of the egg-plasm (p. 216).
2. MORE DETAILED DISCUSSION OF THE PROBLEM OF DETERMINATION.
Self - differentiation and dependent differentiation (p. 219). 0.
Hertwig's directly formative influence of exterior causes, and
Zur Strassen's criticism of this theory (p. 220). The respective
functions of preformation and epigenesis in ontogeny. Driesch's
prospective potency and equipotential systems (p. 225).
3. EMBRYOLOGICAL EXPERIMENTS ON THE EGGS OF VARIOUS KINDS OF
ANIMALS AND THEIR RESULTS (p. 228).
4. CONCLUSIONS.
Epigenetic evolution (p. 235). Differential or integral division of
the nuclear substance ? (p. 236). The machine theory or vitalism ?
(p. 238). Inadequacy of the machine theory of life (p. 238).
Driesch's experiments on Clavellina (p. 245). The problem of life
demands a vitalistic solution (p. 247).
INTRODUCTION AND SURVEY OF THE VARIOUS TYPES OF
CLEAVAGE
LIFE is for the student of nature a fact which he must take as
his starting point for the further investigation of the pheno-
mena of life. All attempts to account for the origin of life
from inorganic matter by way of spontaneous generation have
failed, as they contradict what modern cytology teaches.
This has been shown clearly in Chapter VII. Organic chemistry
may make a bold and triumphant advance by means of the
laborious and ingenious experiments, by which she examines
the elementary composition of living organisms and the
chemical processes of their metabolism. She may succeed
eventually in producing synthetically a highly complex mole-
cule of albumen in her test-tubes, but one thing will always
be wanting to the artificial product, viz. life.
The laws of inorganic matter apply also to living creatures,
but in their case the laws are subordinate to a higher unity,
which brings their activities into that wonderful harmony,
tending to fulfil a purpose, that we call a vital process.
207
208 MODERN BIOLOGY
Even in the simplest unicellular organisms, Amoebae and
Bacteria, we encounter the mysterious problem of life. We
meet with it in a more astonishing form in the fertilised egg-
cell, out of which a multicellular plant or animal is produced
by a long series of cell- divisions. In Chapter VI we have
traced the microscopical processes that go on within the
germ-cells, before their union in the fertilised ovum. Now let
us consider the following deeply important questions con-
cerning the continuation of the same great problem of life : —
1. How does the organism, in its individual ontogeny, de-
velop from the egg-cell into a perfect animal or plant ?
2. How have the organisms on our earth been evolved,
each according to its kind, from the first appearance
of life in the world to our present Fauna and Flora?
In this chapter we can deal only with the first of these
questions, leaving the other for subsequent discussion.
It will conduce to a better understanding of the following
arguments if we begin by studying the chief kinds of cleavage
in animal ova.1
After fertilisation is effected, the egg-cell divides rapidly
into 2, 4, 8, 16, &c., cells, which become smaller as the process
of cleavage continues. These cells are called cleavage-spheres
or Uastomeres. We speak of each egg as having an animal
and a vegetative pole, inasmuch as the substance at one pole
serves chiefly to form the animal organs or nervous system,
and that at the other pole serves chiefly to form the vegetative
organs or digestive tract.
Different types of cleavage processes are distinguished ;
the peculiarities of which depend upon the quantity of food — •
yolk or deuteroplasm in the egg, and upon its position.
The cleavage of the egg is total or partial, according as the
whole substance of the egg, or only part of it, undergoes the
process of cleavage. It is total in eggs poor in yolk, partial in
those rich in yolk, as the yolk impedes cleavage. In total
cleavage the whole substance of the egg is used to build up
the embryo, and therefore eggs that show this type of cleavage
are called holoblastic, whilst those with partial cleavage are
called meroblastic. In holoblastic eggs with total cleavage,
1 For further details see R. Her twig, Lehrbuch der Zoologie, 1905, pp 125, &c.
(Eng. trans, pp. 151, &c.),
THE PEOBLEM OF DETERMINATION 209
it is either equal or unequal, according as the cleavage-spheres
are equal or unequal in size ; this depends upon the quantity
of yolk in the egg.
In meroblastic eggs with partial cleavage, it is either
discoidal or superficial. This distinction depends upon the
position of the yolk in the egg. If the yolk is accumulated
about the vegetative pole, the cleavage is limited to the animal
polo (discoidal cleavage) ; if the yolk lies in the centre of the
egg, only the surface of the egg shows a thin layer of cleavage
cells surrounding the unsegmented central mass (superficial
cleavage).
The eggs which have their yolk more or less concentrated
at the vegetative pole are called telolecithal ; those with a
mass of yolk in the centre are called centrolecithal.
Superficial cleavage occurs among arthropoda and especially
among insects. Discoidal cleavage occurs in birds and in
most of the other vertebrates, among molluscs, also in cuttle-
fish, and in some Arthropoda and Tunicata. Equal and
unequal cleavage, however, may appear in all kinds of multi-
cellular animals.
The account just given of the different types of cleavage
does not depend immediately upon the question whether
preformation or epigenesis controls the cleavage of the egg.
We shall have to study the behaviour of animal eggs towards
these two factors in development in the third part of this
chapter.
1. THE PROBLEM OF DETERMINATION AND ITS HISTORY
It was chiefly through Karl Ernst von Baer (1791-1876)
that the study of the individual development of animals became
a special branch of zoology, to which the name ontogeny has
been given. There is an analogous branch of botany, dealing
with the individual development of plants.1
Both confront us with the same old and yet ever new
questions with which from remote antiquity the minds of
ordinary men have busied themselves, no less than the inquiring
spirit of the scholar. Why are children like their parents ?
1 See the general sketch of the departments of biological science, Chapter I,
pp. 3, &c.
p
210 MODERN BIOLOGY
Why does an oak always grow out of an acorn, and why is a
chicken always hatched out of a hen's egg ? Whence comes
the specific conformity to law in accordance with which, from
the fertilised egg of any given species, there is invariably pro-
duced a being similar to that which gave life to the egg-cell ?
What is the influence determining the germ of the new indi-
vidual to follow one line of development rather than another ?
Moreover, are the laws controlling this development purely
mechanical, or are there also vital laws, essentially superior
to what goes on in inanimate nature ?
These are undoubtedly very interesting and important
questions, having a bearing not only upon biological research,
which is seeking to solve the problem of life by way of natural
science, but also upon philosophy, which is striving to penetrate
into the essential nature of life by means of the phenomena
of life.
We stand therefore face to face with the problem of deter-
mination, i.e. with the question : ' What are the causes con-
trQlling_embr¥onic development ? ' Regarded from afar this
problem may scorn to the layman to resemble a porcupine
bristling with all manner of technical difficulties, so that an
ordinary intellect can scarcely venture to approach it. Let me,
however, see if I cannot succeed in inducing this porcupine
of the problem of determination to lay down his prickles, and
show himself to my readers in a harmless form, presenting no
particular difficulties to a man of average intelligence.
To begin with, I must follow Oskar Hertwig l in pointing
out that a one-sided view of the subject cannot fail to be a
false one. Many internal and external causes co-operate in
the development of organic beings, and they do so in such a
way that the internal causes are invariably the foundation for
the action of the external factors.
The problem that we have to discuss is closely connected
with the subject of Chapter VI, viz. the relation of the pro-
cesses of cell-division to the problems of fertilisation and
heredity. We came to the conclusion that the chromatin
constituents of the nuclei of the germ-cells, that is to say their
chromosomes, might with great probability be regarded as the
chief material bearers of the phenomena of heredity, and
1 Allgemeine Biologie, pp. 132, &c., and 138, &c.
PBEEOKMATION OB EPIGENESIS ? 211
consequently also as the chief bearers of the laws governing
the particular development of each kind of animal and plant.
Yet in making this statement, we have alluded to only
one side of the problem of organic development, viz. to that
which is the subject of microscopical cytology. We now
encounter a series of other questions which are of great interest
as affecting the problem of life : — Does the development of^tho
fertilised ovum depend upon a self-differentiation, controlled
exclusively by the interior factors already present in the egg,
or does it depend upon a differentiation controlled chiefly _by
exterior causes ? Must we uphold the theory of preformation,
which assumes that there is in the egg a foreshadowing of the
whole future being, or the theory of epigenesis, which asserts
that the organs of the embryo are formed afresh in the course
of its development ? The so-called problem of determination
is comprised in the answers to these questions. It will be well
to show shortly what success has hitherto attended the attempts
made to solve it. Incidentally we shall have to be careful to
ascertain whether the individual development of organic beings
is controlled by some special laws of life, as vitalism asserts, or
whether it can be satisfactorily explained, as the mechanics
theory maintains, by merely chemico -physical causes.
The branch of biology that deals with experimental research
into the laws and causes of organic formation is known as the
physiology of development. Wilhelm Koux, the principal
founder of this branch of science, called it ' mechanics of
development.' But as the mechanical explanation of the pro-
cesses under consideration is only a part of the problem, we
agree with Hans Driesch, who has done excellent work in this
department of research, that it is better to adopt the name
physiology of development.1
1 Among the publications bearing on this subject I may mention particularly
Das Archiv fur Entwicklungsmechanik der Organismen, edited by W. Roux
in Halle a. S. Also W. Roux, ' Einleitung zu den Beitragen zur Entwick-
lungsmechanik des Embryo ' (Zeitschrift fur Biologic, XXI, 1885) ; Die
tinttvicklungsmechanik der Organismen, eine anatomische Wissenscha/t der
Zukunft, Vienna, 1890 ; Die Entwicklungsmechanik, ein neuer Zweig der
biologischen Wissenschaft, Leipzig, 1905. E. Pfliiger, ' t)ber den Einfluss der
Sehwerkraft auf die Teilung der Zellen und auf die Entwicklung des Embryo '
(Archiv fiir die gesamte Physiologie, XXXII, 1883) ; ' Beitrage zur Entwick-
lungsmechanik des Embryo ' : No. 1. ' Zur Orientierung iiber einige Probleme
der embryonaleii Entwicklung ' (Zeitschrift fur Biologie, XXI, 1885) ; ' tJber
die Bestimmung der Hauptrichtungen des Froschembryo im Ei und iiber die
p 2
212 MODEKN BIOLOGY
It may appear to some readers that these questions have
already been answered satisfactorily by the results previously
described of microscopic morphology. Among the higher
organisms at least, under normal circumstances, the development
of a new individual can result only from fertilisation, which
consists essentially in the union of the nuclei of the ovum and
spermatozoon, as we saw at the end of Chapter VI (pp. 156, &c.).
As the chromosomes of the nuclei of the germ-cells are the
bearers of heredity, visible under the microscope and passing in
definite number and order from the parents to the children,
and as (according to Boveri's theory of the individuality of the
chromosomes) they preserve some amount of independence
during the whole process of development, it may seem a
superfluous question to ask whether the development of the
fertilised ovum depends upon preformation or epigenesis,
upon an independent or a dependent differentiation. Has not
erste Teilung des Froscheis ' (Breslauer drztliche Zeitschrift, 1885). 0. Hertwig,
' tiber den Wert der ersten Furchungszellen fiir die Organbildung des Embryo '
(Archiv fiir mikroskopische Anatomie, XLII, 1893) ; Zeit- und Streilfragen der
Biologie, I, Jena, 1894 ; Prdformation oder Epigenese ? II, 1897 ; Mechanik
und Biologie ; Die Zelle und die Gewebe, II, Jena, 1898 ; Allgemeine Biologie,
Jena, 1906 (especially recommended). A. Weismann, Das Keimplasma,
Jena, 1892 ; Vortrdge uber Deszendenztheorie, Jena, 1902 (Lectures on the Theory
of Evolution, Eng. trans.). E. B. Wilson, * Amphioxus and the Mosaic Theory
of Development ' (Journal of Morphology, VIII, 1893). H. E. Crampton,
* Experimental Studies of Gastropod Development ' (Archiv fiir Entwicklungs-
mechanik, III, 1896). C. 0. Whitman, 'Evolution and Epigenesis' (Wood's
Hall Biological Lectures, 1894). Hans Driesch, Analytische Theorie der organ-
iftchen Entwicklung, Leipzig, 1894 ; Die orga nischen Regulationen, Leipzig, 1901 ;
* Kritisches und Polemisches ' (Biolog. Zentralblatt, XXII, 1902, Nos. 5, 6, 14,
15 ; XXIII, 1903, Nos. 21-23) ; ' Ergebnisse der neueren Lebensforschung '
(Politisch-Anthropologische Revue, II, 1903, part 10). 0. Herbst, Formative
Reize in der tierischen Ontogenesis, Leipzig, 1901. Th. H. Morgan, Regeneration,
New York and London, 1901. 0. L. Zur Strassen, ' tiber das Wesen der
tierischen Formbildung ' (VerhandL der Deutschen Zoolog. Gesellsch., 1898,
pp. 142-156). K, Heider, ' Das Determinationsproblem ' ( VerhandL der Deutschen
Zoolog. Gesellsch., 1900, pp. 45-97). L. Kathariner, * Uber die bedingte Unab-
hangigkeit der Entwicklung des polar differenzierten Eis von der Schwerkraf t '
(Archiv fiir Entwicklung 'smechanik, XII, 1901, part 4) ; ' Weitere Versuche
iiber die Selbstdifferenzierung des Froscheis ' (Ibid. XIV, 1902, parts 1 and 2) ;
' Schwerkraf twirkung oder Selbstdifferenzierung ? ' (Ibid. XVIII, 1904, part
3, pp. 404-414). An excellent general account of the problem of Determination
is given by Korschelt and Heider in their Lehrbuch der Entwicklungsgeschichte
der wirbeltosen Tiere, Allgem. Teil, I, Jena, 1902, § 1, cf. especially chapter ii,
4 Das Determinationsproblem ' (pp. 81-150). In the same book will be found
a list of all the literature on the subject up to the year 1902 ; for works published
since that date see 0. Hertwig, Allgemeine Biologie. Of botanical works
dealing with embryology I may mention particularly : W. Pfeffer, Pflanzen-
physiologic, I, Leipzig, 1897 ; II, first part, 1901. Also G. Klebs, « Uber
Probleme der Entwicklung ' (Biolog. Zentralblatt, XXXIV, 1904, Nos. 8, 9, 14,
15, 16, &c.).
THE PKOBLEM OF DETEKMINATION 213
this question been already answered in what has gone before, and
have we not already decided in favour of preformation, and
of independent differentiation ?
The matter is not so simple as it appears. Even if we
assume that the chromosomes of the nuclei of the germ-cells
are the chief material bearers of heredity, passing on from one
generation to another, we still have to solve the problem of
the development of the organism from the fertilised ovum.
This difficult question still remains : * What causes the groups
of cells, formed out of one egg-cell by cleavage-division, to
differ from, one another more and more, both morphologically
and physiologically, as the development of the embryo pro-
ceeds ? How is it that these groups of cells develop into the
various tissues and organs of one and the same individual ? '
In other words : * What causes underlie the process of harmo-
nious differentiation, by means of which the wonderful and
complicated structure of the complete organism with all
its manifold parts is produced from the apparently simple
ovum ? '
The physiology of development, which we now have to
study, approaches this problem on lines quite unlike those
followed by microscopical anatomy. The latter has recourse
to modern methods of staining and cutting sections, and
examines the tissues and cells of animals under the strongest
microscopes, and strives to trace all the morphological changes
in the nucleus and cytoplasm of the cells, but the former
proceeds by way of actual experiment. It takes, for instance,
the living ovum of a frog, subjects it to all possible kinds of
artificial treatment, to pressure, twisting, division or partial
destruction of its cleavage-spheres, and then observes how
the embryo develops under these conditions. From
these observations it draws its conclusions regarding the
laws and causes of the embryonic development of living
creatures.
It proceeds also to study the course of regeneration in the
living organism by similar methods. It tries experimentally,
in the case of a creature that has reached an advanced stage
of development, how far, and in what way, the faculty is re-
tained of forming afresh lost organs and tissues. The experi-
ments made by G. Wolff and others with a view to determining
214 MODEKN BIOLOGY
the power of regeneration in the lens of the eye of a salamander
have become particularly famous.1
Before we discuss the results of modern research in em-
bryology, we must refer shortly to the previous history of the
problem of determination.3
The question whether the future individual is contained
in the egg, and, if so, under what form, has aroused the interest
of students in all ages, although until recent times there has
been very little certain knowledge upon which to found any
theory. In the seventeenth and eighteenth centuries the
most eminent scientists, such as Swammerdam, Malpighi,
Leeuwenhoek, Haller, Bonnet and Spallanzani declared them-
selves to be in favour of the preformation theory, then known
as the doctrine of evolution, or unfolding.3
They observed the development of the butterfly in the pupa,
and the blossom in the bud, and laid down the dictum : ' Evolu-
tion is merely the unfolding of parts already present in the egg-
or sperm-cell, but imperceptible to us by reason of their
diminutive size and transparency.' It is true that we can
trace in the pupa all the organs of the future butterfly, and in
the ripe bud all the parts of the future flower, but when this
theory of unfolding is applied to the embryonic development
of living creatures, it leads to very peculiar results. According
to it, in the first ovum of each species 4 all the individuals of
all the succeeding generations must have been contained in
infinite numbers and in infinitely diminutive size. For instance,
the ova of the first cat must have contained extremely small
editions of all the future cats that would ever be born to the
1 G. Wolfi,Entwicklungsphi/siologische8ludien,I, 1895; Die Regeneration der
UrodelenUnse. Cf. also Part II, 1901, and Part III, 1905, of the same series
of studies in the Arcliiv fur EnttvicMungsmechanik. Hans Spemann, ' Uber
Linsenbildung nach experimenteller Entfernung der primaren Linsenbildungs-
zellen ' (Zoolog. Anzeiger, XXVIII, 1905, No. 11, pp. 419-432). A list of the
other works on this subject by Barfurth, Colucci, Fischel, Herbst, Lewis,
Mencl, E. Miiller, Schaper and Spemann will be found in Spemann, p. 432.
Cf. also 0. Hertwig, Allgemeine Biologie, pp. 546, &c.
2 Cf. 0. Hertwig, Allgemeine Biologie, pp. 350, &c.
3 At the present day we generally speak of the theory of evolution with
reference to the evolution of the species, not with reference to that of the
individual. In order to avoid confusion, I have used the expression ' theory
of preformation ' to designate the theory of evolution in the earlier sense.
4 Or in the first spermatozoon, for, according to the theory of the animal-
culists, it was not the egg-cell, but the sperm-cell, which transmitted hereditary
qualities. See p. 104 and p. 158.
THEOKY OF EPIGENESIS 215
end of the world. This has also been termed the theory of
embpitement.
In 1759 Kaspar Friedrich Wolff in his ' Theoria generationis '
for the first time opposed the old theory of preformation, and
by so doing became the founder of the theory of epigenesis.
After a careful examination of the development of a chicken,
he came to the conclusion that the egg was only a mass of
unorganised matter, which was gradually organised in the
course of the development of the embryo. Wolff's opinion
is right to this extent, that the organs of the embryo are really
formed anew, because the fertilised egg (as was recognised
only in the nineteenth century) still has the character of a
simple cell, and so cannot consist of organs. But Wolff was
wrong in thinking the egg a mere mass of unorganised matter,
for modern microscopical research has revealed to us the
wonderfully delicate structure of the egg-cell and its nucleus,
and has shown us the chromosomes, which, being definite
parts of the nucleus, are the material bearers of heredity, and
are distributed with such marvellous exactitude among the
cleavage-cells of the egg as it develops. I will not, however,
at this point anticipate the historical development of the
problem of determination.
As the study of embryology advanced in the first half of the
nineteenth century, the theory of epigenesis found increasing
favour, and soon became predominant.
In 1853, Eudolf Leuckart, a famous zoologist, wrote
in his article on procreation : * Our knowledge of the develop-
ment of the embryo and of the formation of the ' procreative
substance admits of only one interpretation, viz. in the sense
of epigenesis — there can be no further doubt on the subject ;
the embryo is the product of a new formation in connexion
with the procreative substance.'
As late as the year 1872, Ernst Haeckel in his * Anthropo-
geny ' described the human embryo in the so-called monerula
stage l as a ' completely homogeneous, structureless mass,'
1 We owe the ' discovery ' of this stage in the embryonic development
of man to a mistake on Haeckel's part. He believed, though wrongly, that
the germinal vesicle of the embryo broke up as soon as embryonic development
began. According to Haeckel's fanciful anthropogeny, the monerula stage
in the human germ is a lineal repetition of the monera stage of our most remote
ancestors. As a matter of fact, not only is this monera stage existent only
216 MODEEN BIOLOGY
as a ' simple lump of primitive matter.' Haeckel must certainly
have studied the human embryo through very cloudy glasses, if
in the year 1872 he was still able to see so little of its finer
histological structure, although Goette fared no better in 1875,
when he studied the egg of the toad, and declared it to be an
unorganised lifeless mass, produced by a transformation of
one or more germ- cells.
The theory of epigenesis, however, was not destined to
stand its ground much longer. As microscopes became more
perfect, both the ovum and the spermatozoon were seen to
contain elements of very complicated composition, which had
to prepare, by a special process of maturation, for the
union of their nuclear substances, effected by fertilisation.
At once the breath of popular favour veered round to the
preformation theory, although it was no longer the old theory
of emboitement, but assumed an entirely new form.
In 1874 Wilhelm His l propounded the theory of there being
gerrnregions or local areas for the formation of organs in
theTincRviduaT. development of vertebrates.2 According to this
theory definite tracts in the fertilised ovum are, in virtue
of some special interior tendency or Arilage, destined to
form definite organs in the embryo. At the same time he
submitted Haeckel's fantastic ideas on human embryology
to a most destructive criticism in his article. The new
theory of germ-regions for the formation of organs found
support in observations made on many other animals, and it
was discovered that even in the ovum the so-called primordial
axis gave rise to an animal and a vegetative pole, determining
the direction in which the future embryo was to develop.
Embryology had therefore again taken an appreciable turn
in the direction of the preformation theory.
But in 1883 there was an apparent reversion to epigenesis,
in consequence of the experiments made by Edward Pfliiger,
with a view to determining the influence of gravitation upon
in the imagination, but so is also the ontogenetic moncrula stage in the develop-
ment of the human embryo. For a criticism of Haeckel's pedigree of man
see Chapter XL
1 Unsere Kdrj)erform und das physiologische Problem ihrer Entstehung, Leipzig,
2 Wilson suggests ' Germinal Localisation ' as a name for this theory. —
Translator's Note.
ISOTKOPY OF EGG-PLASM 217
the development of frogs' eggs. To these experiments we owe
Pfliiger's principle of the isotropy of the egg-plasm, according
to~~~which all the protoplasmic" constituents of the egg are
collectively of equal value with regard to the formation of the
organs in the embryo. Pfliiger put frogs' eggs in what he called
a position of constraint, so that the egg was prevented from
turning round in its gelatinous envelope, owing to defective
swelling of the latter. Under normal circumstances the
animal half of the frog's egg, which consists of lighter sub-
stances and contains black pigment, always is uppermost,
whilst the pale yellow vegetative pole is underneath. If,
however, the egg is prevented from turning, the axis of the egg
can be made to form any desired angle with the vertical. Even
in this case the first cleavage-plane of the egg as it develops
will always be vertical. This might lead us to believe that
gravitation alone determined the arrangement of the parts
of the embryo, and that it was a matter of indifference
which part of the egg lay above or below at the beginning
of cleavage.
The conclusions, which Pfliiger deduced from this fact in
favour of the isotropy of egg-plasm, proved, however, not to
be tenable. Wilhelm Koux and Oskar Hertwig soon suggested
that the dependence of the evolution of the frog's egg upon
gravitation was only a consequence of the unequal specific
gravity of its parts. In the eggs placed in abnormal positions
the egg envelope was prevented from turning, but the_rearrange-
Tnopj^pf f]]^ substances within the egg was unaffectejj. Born
proved this by experiments of his own.
In order to disprove Pfliiger's theory of the importance of
gravitation in directing the development of the embryo,
Koux placed some frogs' eggs, already developing, on a disc
that rotated vertically, so that their position with regard to
gravitation was constantly changing. In spite of this, their
development was normal both as to time and manner. Yet,
as Kathariner has recently pointed out,1 in his clinostatic
experiments Koux had replaced the force of gravitation by
1 Uber die bedingte Unabhangigkeit des polar differenzierten Eis von der
Schwerkraft ' (Archiv fiir Entwicklungsmechanik, XII, 1901, Part 4, pp. 597-
609) ; ' Weitere Versuche liber die Selbstdifferenzierung des Froscheis '
(ibid. XIV, 1902, Parts 1 and 2, pp. 289-299) ; ' Schwerkraftwirkung oder
Selbstdifferenzierung ? ' (ibid. XVIII, 1904, Part 3, pp. 404-414).
218 MODEKN BIOLOGY
another force, viz. the centrifugal ; and consequently it was
still not certain that the development of the egg was completely
independent of an external directive force.
In order to settle this point, Kathariner had recourse to
another method. He kept the fertilised frogs' eggs in constant
rotation by means of a stream of water. Even then they
developed in a perfectly normal way, although somewhat
more slowly than usual. These experiments have proved
conclusively that the reasons for the specific development jof
a frog's egg into a frog are in the egg itself, and cannot be found
in any external influences. The development of the egg
depends on self-differentiation, as Koux declared. We must
regard as disproved, once for all, the theory which Pfluger
enunciated as follows, in support of epigenesis : ' I am of
opinion that the fertilised ovum no more bears an essential
relation to the subsequent organisation of an animal, than the
snowflakes do to the size and shape of the avalanche to which
they contribute : the fact that out of a germ the same thing
is always produced is due to its being always subjected to
the same external conditions.'
2. MORE DETAILED DISCUSSION OF THE PROBLEM
OF DETERMINATION
When we find scientific men like Oskar Hertwig,1 who are not
far from being vitalists, still feeling bound to ascribe to external
factors, such as heat, the rank of causes of specific development,
we must believe that this is due to a confusion of the general
conditions of development with its particular causes. We have
many external means of accelerating or retarding development,
and of making it follow a normal or an abnormal course, but
we are never able to alter the laws of specific development, for
instance in the frog's egg. If, therefore, such an egg invariably
produces a frog, it does so through some self-differentiation in
the fertilised ovum.
If we regard the egg with its capacity for development
as a ivhole, the question whether preformation or epigenesis
controls its action is therefore already answered in favour of
1 Die Zelle und die Gewebe, II, 1898. Cf. my remarks on 0. Hertwig's
opinions on p. 220.
THEOKY OF PKEFOKMATION 219
preformation ; there are in the egg some dormant tendencies
which underlie its specific development. But this is not a
complete solution of the problem of determination.
We have to answer another and a much more difficult
question: 'In what relation do the individual parts of the
fertilised ovum stand to one another ? Is their development
fully independent, based on self -differentiation, or is it in a
state of regular dependence upon the other parts of the egg,
and based, therefore, on a dependent differentiation ? '
. I have already discussed Pfluger's theory of the isotropy
of egg-plasm, according to which all parts of the egg are quite
uniform in material and in their influence on the development
of the various organs of the embryo (see p. 217). This
theory must be given up, for, as Eoux pointed out, even before
cleavage begins, the median plane of the future embryo is
determined by the position of the cleavage-nucleus in copulation,
i.e. by the course taken by the male pronucleus in order to
unite with the female pronucleus, and so form the cleavage
nucleus of the fertilised egg. Kecent microscopical research
has revealed the regular distribution of the chromatin of the
cleavage-nucleus to the daughter-cells of the egg, and this
distribution introduces the development of the embryo. We
must therefore ascribe to the chromosomes of the nuclei an
important part in determining the formation of the organs in
the embryo. This consideration gives support to Koux and
Weismann's theory of nuclear regions for the formation of
organs. Here too, therefore, the theory of preformation seems
to prevail over epigenesis.
In fact, epigenesis seems almost hopelessly weak as a theory,
if we take into account only those epigenetic opinions which
are based on mechanics, and aim at accounting for the whole
development of the embryo merely by the attraction and
pressure of the cleavage-spheres. But the chief supporters of
epigenesis — men like Oskar Hertwig and Hans Driesch —
are by no means adherents of the theory of mechanism in the
ordinary sense of the word. Oskar Hertwig's views on the
subject of organic development have much in common with
vitalism ; he has expressed them in his earlier works, but a
concise statement of them may be found in his * Allgemeine
Biologie,' 1906, which is practically a new edition of his previous
220 MODEEN BIOLOGY
textbook ' Die Zelle und die Gewebe ' (' The Cell and the
Tissues ') published in 1898.
In discussing the various internal and external causes of
development (pp. 132-140), he says that both factors must
co-operate in every process of development ; but, as he thinks
the internal causes (or tendencies to development) always
form tEe basis for the action of the external influences, it is
impossible to say that he gives a purely mechanical explanation
of the process of development. On the contrary (pp. 141, &c.),
he expressly emphasises the ' very important differences
existing between machines and organisms, between what is
mechanical and what is organic.' In his ' Allgemeine Biologie '
he devotes only two chapters (xx and xxi) to the external
factors of organic development, but no less than four chapters
(xxii-xxv) to the internal factors, and ascribes to them the
chief importance, especially in the case of animals (p. 508).
He expresses himself as a vitalist in speaking of the various
stages of the process of development, and says (p. 519) : * The
form at any given moment appears to be in many respects a
function ot the growth of the_organic substance ; its persistence
is subject to definite conditions ; and as they change in con-
sequence of advancing growth, they effect a modification,
adapted to the purpose in view, in the form of the substance,
which is capable of reacting under their influence.'
At the close of this chapter I shall recur to Oskar Hertwig's
attitude towards vitalism. In 1898 he felt bound to ascribe to
external mechanical causes l a direct formative influence upon
the process of development in many cases, but in 1906 he
modified this opinion considerably. His earlier views were
challenged by 0. L. Zur Strassen in a lecture delivered on
June 3, 1898, at the eighth meeting of the German Zoological
Association at Heidelberg.2
According to 0. Hertwig, the division of the fertilised ovum
into cells of equal size and similar structure is effected by the
vitelline contents of the cells and the external shape of the
cleavage-spheres (blastomeres). He thinks that the delicate
mechanism of mitotic karyokinesis, in which the egg changes
into the groups of cells in the embryo, is the cause of
cell-division as such, but not of the differentiation of these cells
1 Die Zelle und die Gewebe, II.
2 ' tfber das Wesen der tierischen Formbildung ' (VerJiandl, pp 142-156).
HERTWIG'S MECHANICAL LAWS 221
to form organs and tissues, although the two processes are
connected. Hertwig attempts to account for unequal cell-
division by means of the mechanical influence of the yolk
contained in the egg, which, he thinks, causes the daughter-
cells to be of different sizes. If more deuteroplasm is accu-
mulated at one pole of the egg than at the other, the nucleus
of the egg-cell is, according to Hertwig, mechanically pushed to
the opposite pole, and the result is the division of the egg into
two cleavage-spheres of unequal size.
Eeasonable as this may sound, the rule still does not
universally hold good, and there is not a purely mechanical
regularity in the process of cell-division. There are, fof
instance, as Zur Strassen points out, a number of cases (e.g. in
the cleavage of the egg of the maw- worm, Ascaris) where the
actual process is the direct reverse of that required by Hert-
wig's 'law.' In this particular egg, when the first cleavage-
spindle is formed, the upper part of the plasm is pale in colour
and poor in yolk ; whilst the lower part is rich in yolk. Never-
theless, after the cleavage the upper daughter-cell is the larger,
and the lower is the smaller, in spite of its abundance of yolk.
0. Hertwig attempted to give a very simple account of
the uneven rate of division of the cleavage-spheres by means
of the mechanical action of the yolk. He thought that cells
containing much yolk divided more slowly than those contain-
ing less, because the yolk offered an external resistance to the
cleavage processes of the protoplasm. But here, too, there are
facts in direct opposition to Hertwig's mechanical law. Accord-
ing to Jennings, in the development of the Kotifer Asplanclma
and of many other species, the larger cells, that are rich in yolk,
have a decided tendency to divide more quickly than the
smaller cells, that are poor in yolk.
Purely mechanical factors must by their very nature always
act in the same way, and these ' exceptions ' to Hertwig's
mechanical laws show that the laws, even where they are
apparently observed, are not purely mechanical, but a vital
conformity to law underlies them, controlling and regulating
tneaction of the mechanical factors.
Of still greater importance for the decision of the question
whether the development of the organism can be accounted
for on purely mechanical grounds, is the regular direction in
which the cells of the embryo divide, for all growth in a definite
222 MODEKN BIOLOGY
direction is accompanied by a corresponding formation of the
nuclear figures in the processes of mitotic division, and there-
fore the series of cleavage stages in the developing embryo is
based primarily upon that definite direction of division. If
it were possible to find a purely mechanical principle to account
for this, it would go far towards enabling us to explain the
processes of development on mechanical lines. Oskar Hertwig
thought that he had discovered a principle of this kind, and
enunciated the following ' law ' regarding it : ' The division -
spindle of the cell is, in the case of non-spherical cells, placed
in the direction of the largest mass of protoplasm, i.e. in the
longest axis of the cell.'
From the purely mechanical point of view this is quite
natural, and there are in fact many cases of agreement with
this law — but there are, on the other hand, a great many other
facts that contradict it.
As Zur Strassen points out, it is easy to bring forward an
overpowering number of instances in which the division-
spindle does not follow the longest axis of the cell, which would
be a convenient and natural arrangement from the mechanical
point of view, but it follows a shorter axis, often the shortest
possible, so that it seems to challenge the greatest pressure
instead of avoiding it, as it should do, if Hertwig's mechanical
theory were correct. This occurs in all cylindrical epithelia
and also in very many of the early blastula stages of various
organisms.1
With regard to the cleavage stages of the embryo, it has
been conclusively shown by Jennings in the case of a Kotifer,
Asplanchna, by Conklin in the case of a snail, Crepidula, by
Bergh in various Crustacea, and by Sobotta in the lancet
fish, Amphioxus, that there is no such thing as a direct in-
fluence of the shape of the cell upon the direction of the spindle
that is easily explicable on mechanical lines. There is therefore
no justification for Hertwig's ' mechanical law,' as stated
above.
1 By the blastula stage we understand the first development of the embryo,
in which the ectoderm is formed as a hollow sphere consisting of one layer
of cells. The next is the gastrula stage, in which, by means of invagination
of part of the blastula, the intestine is formed and the entoderm begins to
grow. Between ectoderm and entoderm there is formed subsequently a
third layer of cells, called the mesoderm.
ZUR STRASSEN'S EXPERIMENTS 223
Still less is there any justification for a theory propounded
by J. Loeb, an American. He thinks that the regular inter-
action of the parts of the embryo depends upon the mechanical
pressure exercised upon one another by the crowded cleavage-
spheres, forcing them by merely external means to assume
a definite geometrical form. Such crude attempts at explain-
ing facts on mechanical lines are almost as unsuccessful in
embryology as in animal psychology.1
Zur Strassen has arrived at the following conclusion : — •
' That the cell in its living plasm contains mechanisms enabling
FIG. 27.
sp = spindle.
it independently to discover and adopt a definite direction in
division, corresponding to the aim of its ontogeny.'
He proved this by experimenting with the eggs of the
maw-worm, Ascaris. The second cleavage-division affords
a classical instance of the formation of the spindle (sp) in the
shortest axis of the cell (fig. 27).
If there were only purely mechanical causes forcing the
protoplasm to set the spindle in this position, it ought to be
easy to induce the lower cell, which is subject to greater
pressure than the upper (see fig. 27), to develop its spindle
on its longest axis, when the pressure is removed. In order
to effect this, Zur Strassen rolled the eggs to and fro under a
glass until they were no longer spherical, but of a long oval
1 On the latter see the author's article ' Zur mechanischen Instinkttheorie '
(Stimmen aus Maria-Loach, LX, 1901, parts 2 and 3). Also Instinkt und
Intelligenz im Tierreich, 1905, chapter viii. A criticism of Loeb's chemico-
physical theory of fertilisation may be found on pp. 147, &c.
224
MODEBN BIOLOGY
shape, and thus the two cleavage-cells had room enough to
develop their spindles in the longest diameter. But they did
not do so ; in the lower cell also the spindle retained its normal
position, although it was in the shortest axis of the cell. Similar
observations were made by Zur Strassen at the two-celled
stage of the giant eggs of Ascaris, which have a long, oval
shape, and their cleavage-spheres are so far from being subject
to any mechanical pressure that they float freely within the
FIG. 28.
covering of the egg, and touch one another at one point only.
Yet even in this case the two cells developed their spindles
in the shortest axis (fig. 28).
These experiments in embryology lead us chiefly to the
negative result, that the rj^echanicana^ws^idLdQWjQLby_Hertwig,
Loeb, and others arejnag^rate, anH^supply no causal explana-
tion of the processes we are discussing. Zur Strassen thought
that his experiments justified the positive conclusion : ' That
the cell, when ready to divide, contains most delicate mechan-
isms which determine the moment when mitosis shall take
place, the direction of the spindles, and the comparative size
of the products. This really seems as if the cleavage-cell
possesses an unerring instinct directing the process of cleavage.'
QUESTIONS KEGAKDING ONTOGENY 225
Therefore not only do the causes determining the specific
development reside in the egg itself, but the interaction of
the various parts of the egg, as it develops, is controlled by a
teleological law, which directs the mechanical factors towards
the aim of the embryonic development.
This has brought us at least somewhat nearer to a solution
of the problem of determination, but we have still not decided
whether preformation or epigenesis underlies the whole process
of development. Weismann, the extreme supporter of the
theory of preformation, says that ontogeny can be explained
only by evolution, and not by epigenesis.1
Oskar Hertwig, on the contrary, asserts : 2 ' The develop-
ment of a living creature is by no means a piece of mosaic
work, but all the various parts develop always in relation to
one another, or the development of any one part is always
dependent upon the development of the whole.'
Here, as in every case where scientists hold different opinions,
we must put the question in a clear and definite form, in order
that we may know what each of these theories involves.
We shall therefore ask with Korschelt and Heider : 3 ' Are
there present in the egg, when it begins to develop, any special,
independent Anlagen or fundaments, which develop quite
apart from the other portions of the egg and become definite
formations in the embryo ? And, if there are such Anlagen,
how have they come into existence ? Can other Anlagen of a
similar kind arise later ?
' Or : Do the various formations in the embryo never
develop independently ? Are they always dependent upon
the other parts of it ? In this case we should have to acknow-
ledge the existence of a constant, mysterious influence exercised
by the whole upon its several parts.
* Or : Do both methods of formation, the dependent and
the independent, participate in the development of the embryo ?
and, if so, to what extent ? '
In the first case, if preformation alone controls development,
1 Das Keimplasma, Jena, 1892, p. 184. In his recent lectures on the
Evolution Theory, 1902, Weismann still maintains a decidedly preformistic
attitude, although he concedes a great deal more to epigenesis than he did
previously.
2 Alter e, und neuere Entwicklungstheorien, Berlin, 1892, p. 29. Cf. also his
Allgemeine Biologie, p. 632.
3 Lehrbuch der vergl Entwicklungsgesch., Part I, Jena, 1902, pp. 93-94.
Q
226 MODEKN BIOLOGY
the development not merely of the egg as a whole, but of each
separate organ in the future creature would depend upon self-
differentiation ; it would be mosaic work, and nothing else.
In the second case, if epigenesis alone controls development,
the whole ontogeny of the organism would be based upon
dependent differentiation, upon which the idea of the whole
would be impressed.
In the third case, we should have to trace development
partly to preformation and partly to epigenesis, working
together harmoniously to produce the due result. We might
then follow Driesch in describing the ontogeny of the individual
as an epigenetic evolution. As we shall see presently, this
third alternative is the best, and comes closest to the truth.
The well-known saying, ' What suits one does not suit
another,' is applicable not only to the circumstances of human
lije, but to the phenomena occurring in the development
of living beings. In different kinds of eggs, and in different
stages of the development of one and the same organism,
intrinsic and dependent differentiation act very variously.
We must therefore follow Korschelt and Heider, and examine
the individual cases and the embryological experiments of
modern research. Before doing so, however, I ought to
explain some expressions introduced mostly by Hans Driesch,
the most consistent advocate of epigenesis. In spite of their
learned sound they are all quite simple.
Driesch distinguishes the prospective value and the 'prospec-
tive potency of a cell or a cleavage-segment, in the course of the
development of an individual organism. By prospective value
he understands the real destiny of the cell, by prospective
potency its possible destiny. We may therefore call prospective
value also destiny in development, and prospective potency
possibility in development. We shall understand the dis-
tinction better, if we consider something analogous in human
life. Let us imagine a boy with an Anlage for being a tinker.
If the circumstances of his life permit, and he really becomes
a tinker, it was his prospective value to be a tinker. But the
prospective potency of the same boy was plainly far wider ;
according to his natural disposition he might eventually become
a knife-grinder or a schoolmaster, a gunner or an author. Now,
the prospective potency of a cell comprises all that it is possible
OKGANIC EEGULATIONS 227
for it to develop into, or the sum of the dispositions that it
contains, of which, however, only one or very few can ever
be set in action in the process of development ; these latter
represent the prospective value of the cell and its descendants.
According to Brauer, any cleavage-sphere of the freshwater
polypus Hydra has the power to produce ectoderm and entoderm
cells. But the ectoderm cells of later stages in the develop-
ment of the same animal have lost the power to produce
entoderm cells. Thus in course of ontogeny (or the develop-
ment of the individual) the prospective potency of the cells of
Hydra suffers limitation. In general we may lay down this
principle : The prospective potency of a cell is more lipnitfifj_
in higher organisms than in lower, and in the more advanced
stages of ontogeny than in the earlier ; it may even cease to
exist, and we have an instance of this in the cormfied cells
ofour
Whoever accepts the theory of prospective potency has
practically recognised the truth of epigenesis, for whenever
we speak of the possibility of development, we mean that cells,
or groups of cells, which were originally designed to make up
some definite formation, may, under certain circumstances, take
another direction and serve another end. This process of
transformation has been called redifferentiation or redeter-
mination. In such processes the influence of the whole in some
mysterious way is brought to bear upon the parts of the
organism, and through this influence they co-operate, so as to
develop a creature capable of life. All processes of develop-
ment that have this character are known as regulatory, or as
organic regulations, these being the names used by Driesch.1
Closely connected with Driesch's theory of prospective
potency or possibility of development in cells is his other idea
of the equipotential system. Such a system is formed by a
group of cells, each of which possesses the same potency.
Driesch subdivides these systems into determined equipotential
systems and undetermined or harmonious equipotential systems.
In the former, the number of things that can possibly be made
from the group of cells under consideration is strictly limited.
1 I need not discuss the further distinction, also due to Driesch, between
primary and secondary regulations, primary and secondary prospective
potencies, &c.
Q 2
228 MODEKN BIOLOGY
For instance, from any transverse section of a willow branch
either a shoot or a root may be formed, but the prospective
potencies of the cells of the piece of willow are limited to these
two things. But in the harmonious equipotential systems
any one element can assume any part, and so the number
of possible developments is very great. Each portion of
such a system can likewise accomplish a whole complicated
process of formation ; which form it will assume depends upon
the position borne by the part with regard to the whole, for
all parts are harmoniously subordinated to the whole, whence
the system has its name of ' harmonious equipotential.' Thus,
for instance, each of the cells of the thirty-two cell cleavage
stage in the egg of the sea-urchin is not only able to form the
-^ part of the embryo, which it is its proper function to
form, but, if the 32 cells are artificially separated from one
another, each of them is capable of developing into a very small,
but still complete, sea-urchin larva.
3. EMBRYOLOGICAL EXPERIMENTS ON THE EGGS OF
VARIOUS KINDS OF ANIMALS AND THEIR EESULTS
The scale seems now to be turning again in the direction of
epigenesis, but before pronouncing a final decision, and deduc-
ing conclusions for or against the theories of mechanism and
vitalism respectively, we must briefly consider the various
groups of animals on which embryological experiments have
chiefly been made.
We must mention first the experiments on the eggs of
Amphibia, begun by W. Boux in 1883. With a heated needle
he pricked one of -the first pair of cleavage-spheres of a frog's
£g& and so killed it. The other half, that remained uninjured,
developed exactly as if the destroyed portion had remained
alive, but, as the latter was incapable of development, the
result of the experiment was the production of a half-embryo
(hemiembryo later •alis), i.e. a future frog cut in two lengthwise.
Eoux succeeded also in destroying a cleavage-sphere at the
four-cell stage, and then a three-quarter embryo was produced.
These results justified the conclusion that under ordinary
circumstances the two cleavage-spheres of the two-cell stage
of development in the embryo frog contain the rudiments of
EXPEKIMENTS ON FROGS' EGGS 229
the right and left half of the future frog respectively, and these
rudiments have the power to develop independently of one
another. In the same way, each quarter at the four-cell stage
seemed able to produce a corresponding quarter of a frog,
without being affected by the remaining three quarters.
Eoux formulated his results as follows : ' Normal develop-
ment is from the outset a system of definitely directed processes;
it is intimately connected with the chief directions in which the
embryo develops, so that the first four cleavage-cells do not
merely each occupy the position of a definite quarter of the
embryo, but are capable of producing each its proper quarter
independently.' ' The development of the frog gastrula and
of the embryo resulting immediately from it, is, from the second
cleavage onwards, a mosaic, made up of at least four vertical
pieces developing independently.'
The development of the frog's egg appeared, therefore, to
obey the laws of preformation and intrinsic differentiation, not
those of epigenesis and dependent differentiation, but obviously
it was not permissible to regard this result as applicable gene-
rally to the ontogeny of other organisms. Even in the case of
the frog, Roux observed subsequently that his half-embryos
afterwards grew into complete ones, as the missing half of
the body was supplied by the existent half, by means of the
materials from the cleavage-sphere which was injured by the
operation. A process of redifferentiation set in, changing
the half into a whole embryo — a regulation which unmistakably
aimed at the production of a complete creature, capable
of life. All the theories of preformation and mechanism fail
to account for this phenomenon. """
Oskar Hertwig repeated Roux's experiments on frogs' eggs,
but came to~quite different results. He observed that when-
ever he destroyed one of the first pair of cleavage-spheres,
with one solitary exception, the uninjured half did not produce
a half-embryo, but a complete embryo of half the normal size.
Here, therefore, we find no trace of mosaic work, but only
confirmation of the laws of dependent differentiation, which is
dominated by the idea of the whole.
It was reserved for 0. Schulze and Th. Morgan to give
by their experiments a satisfactory explanation of the apparent
discrepancy between the results at which Roux and Hertwig
230 MODEEN BIOLOGY
had arrived, whilst employing the same methods on the same
object.
Whenever Morgan left the fro_gs' eggs after the operation
in their natural position, i.e. with their black (animal) pole
upwards, the^uninjured halves invariably produced half-
embryos. When he turned them round, so that the white
(vegetative) pole was uppermost, as a rule complete embryos
of half the normal size were developed. In the former case, the
original arrangement of the egg-substance was retained in the
uninjured blastomere, which continued its ordinary course of
development, and only turned into a complete embryo by later
^differentiation. In the latter case, on the contrary, turning
the egg round altered the arrangement of its contents in a way
which led directly to a regulation of the development in accor-
dance with the design of the whole. In neither case can we
dispense with a principle regulating embryonic development.
From the above-mentioned embryological experiments,
and from others of a similar nature, we may conclude that
under normal circumstances the first two cleavage-cells in the
frog's egg possess a different prospective value, inasmuch
as they form each one symmetrical half of the embryo. But
their prospective potency is identical, and equivalent to that
of the egg before cleavage, for each half can produce a whole
embryo. The same is true of the four blastomeres at the
four-cell cleavage stage of the frog's egg. Each is under
normal circumstances designed to give rise only to a definite
quarter of a frog, but if they are separated, each can produce a
complete, though very diminutive creature. At later periods
of embryonic development, however, frQm_the_eight-aell stage
onwards, the cleavage- cells are not any^ Jonger all of the same
value. At this^stage the fouFcehVof the animal half of the
ovum can produce only organs of the animal sphere, and
those of the vegetative half only organs of the vegetative
sphere. The prospective potency of the cleavage- cells of the
Amphibian egg becomes more limited and restricted as develop-
ment proceeds.
We come now to experiments on the eggs of Echinoderms.
In these, as in the eggs of Amphibia, the chief axes of the
embryo are probably determined before the beginning of the
cleavage process, although we do not know with certainty
on what material and structural circumstances this pre-
EMBKYOLOGICAL EXPEEIMENTS 231
formation depends. In the Amphibian egg the different
colouring of the two poles indicates an animal and a vegetative
half of the egg, but in the Echinoderm egg no such difference
in the egg-substance is perceptible.
Among the eggs of Echinoderms, those of the sea-urchin
are particularly well suited for embryological experiments,
and are often chosen for the purpose. In them it is possible
to separate the blastomeres of the egg undergoing cleavage,
not only by means of needles or by shaking the vessel of water
containing the eggs, but the blastomeres can be isolated much
more satisfactorily, as Curt Herbst was the first to discover,
if the eggs are put into water containing no lime. The absence
o:T lime alone suffices to induce the blastomeres to develop
in isolation ; in fact, at somewhat advanced stages in the
development of the embryo, it is only necessary to put it
into water containing no lime, in order to separate the cells
from one another.
The capacity for regulation, or power of redifferentiation in
the cleavage-spheres, is possessed by sea-urchins' eggs in a
very unusual degree, and has led to true triumphs for the
theory of epigenesis. In the eggs of Amphibia only the first
four cleavage-cells of the embryo, if separated from one another,
are capable of producing a fresh, complete embryo ; but in
sea-urchins' eggs this power lasts as far as the blastula stage^
which, according to Hans Driesch's very careful calculation,
consists of j3QB_£fiUs. Each of these 808 cells is equivalent to
all the rest, as far, as its power of development is concerned.
Driesch used a fine pair of scissors to cut up some sea-urchin
embryos at the blastula stage. He cut them in all directions, /
haphazard, and first the raw edges drew together and closed
the wounds, then the piece cut off became a little round blastula,
which followed the normal course of development and finally
produced a perfect, though small, larva (Pluteus) of the sea-
urchin. If the blastula had been left untouched, and had
followed the usual course of development, the cells situated
where the incisions were made would have occupied quite a
different position in the embryo, and would have served to
form quite different tissues ; for instance, they might have
formed the intestine and not the outer skeleton of the body.
Driesch's experiments have proved, therefore, that in the sea-
urchin blastula all the cells are still equivalent to one another
232 MQDEBN BIOLOGY
with regard to their power of development ; each of them can
occupy any position and discharge any function in the formation
of the organism. All the cells of the Echinus blastula are alike
in their prospective potency, and what each cell becomes,
i.e. its prospective value, is determined by its position in the
whole blastula, which is itself already determined by the
direction of its axes. Driesch has, as a result of his experi-
ments, enunciated the statement : ' The prospective value
of the cell is a function of its position.'
The Echinus blastula is a beautiful instance of a harmonious,
equipotential system, in which each part is able to take the
place of any other part, or to become a complete embryo. Just
as the soul of man is wholly in every part of his body, and wholly
in the entire body, so is the power of organic development
in this case present wholly in every part of the embryo and
wholly in the entire embryo. Without a principle regulating
its development and controlling the mechanical factors, this
wonderful unity in multiplicity would be inconceivable. Only
vitalism can offer any satisfactory explanation of this phe-
nomenon ; mechanics cannot account for it.
The further the development of the organs has advanced in
the Echinus larva, the less is the power of redifferentiation
possessed by the individual cells. In this case too, as in that
of the development of the embryo frog, the prospective potency
of each cell is diminished as growth goes on, although in the
sea-urchin it remains unrestricted until the blastula stage is
reached. Driesch remarks that the organs in their original
Anlage or disposition are without exception the result of depen-
dent differentiation in the widest sense, but in their develop-
ment they show intrinsic or self-differentiation in the literal
sense of the word. It seems, then, that here too epigenesis
must be reconciled with preformation, if we are to give any
complete account of the process of development.
Let us now refer shortly to experiments on the ova of
other classes of animals.
In the ova of Hydromedusae (Polypi and Medusae) the
cleavage-spheres, when isolated, behave as do those in the
ovum of the Triton among Amphibia. A cleavage-sphere after
isolation becomes round, and forms a diminutive whole,
continuing its cleavage- divisions and resulting finally in the
EMBBYOLOGICAL EXPERIMENTS 233
formation of a very small, but otherwise normal larva. Zoja
bred perfect Hydroid polypi from isolated blastomeres of the
two- and four-cell stages, but only larvae (Planulae), from those
of the eight- and sixteen-cell stages, and these larvae had no
power of further development. Therefore, we have here
another instance of restriction of the prospective potency in
the cleavage-cells of the embryo, proportionate to the advance
in its development.
A comparison between these embryological experiments
and others, made on the eggs of Ctenophora with tentacles,
will show what great diversities can exist in the laws governing
the development of closely related groups of animals. In
the ova of the Ctenophora a limitation of the prospective
potency^ of the individual blastomeres sets in very early, so
that we are reminded of the mosaic theory. The first experi-
ments were made by Karl Chun, who succeeded in shaking
apart the two blastomeres resulting from the first cleavage of
the ovum of tentacular Ctenophores and in breeding from
them two half -larvae, each possessing four ribs instead of eight
(the normal number), and having only half the usual number
of other organs too. Subsequent research has confirmed
Chun's observations on all essential points, and we may say
that in Ctenophores the first two cleavage-spheres of the
fertilised ovum have each a clearly defined prospective potency ;
each can produce only half a normal organism, whilst among
the true Medusae belonging to the same subdivision of the
animal kingdom, each cell at the sixteen-cell stage is still
capable of producing a complete little larva. The development
of the first pair of blastomeres in the ovum of a Ctenophore is
a genuine mosaic, which depends on self-differentiation, each
half of the ovum being quite independent of the other half.
The same is true of the formation of the fourth and eighth
parts of the embryo, which are produced by subsequent
cleavage-divisions. Not until the ectoderm has grown over the
embryo is any co-operation and reciprocal action perceptible
between the fourth and eighth parts.
The development of the ribs in the embryo of a Ctenophore
is peculiarly interesting. All who have made experiments on
the fertilised ovum of Ctenophore agree in believing that it
can produce eight ribs and no more. As the process of
234 MODEEN BIOLOGY
cleavage goes on, the possibility of producing them is so far
localised, that to each eighth is assigned the task of forming
one rib. As the Anlagen for the ribs arise from the little
cleavage - spheres, or micromeres, of the embryo, which
differentiate themselves from the large cleavage-spheres, or
macromeres, at the sixteen-cell stage, we must say that each
of the eight micromeres possesses the Anlage to form one rib,
and its development is therefore a real intrinsic differentiation.
Although there is no connexion between Molluscs and
Ctenophores, their eggs behave in the same way during the
process of cleavage. Isolated blastomeres continue to divide
as if they were still in union with the whole, and show conse-
quently partial cleavage. It is true that the half- or quarter-
embryos thus produced do not correspond exactly to a half or
a quarter of the organism under observation, but they become
so far complete as to be capable of life, the ectoderm covers
them abundantly, and there are some attempts at forming the
velum of the normal larva. But it has proved impossible to
breed these creatures any further ; they died in every case at
this point. The development of the Mollusc ovum depends,
therefore, essentially upon self-differentiation of the individual
blastomeres, and can be described as a mosaic. An equally
pronounced mosaic character is displayed by the cleavage
process of the ovum of Annelida and Nematoda.
Chabry's experiments on the egggjof Ascidia seemed also
to support the mosaic theory and preformation, for by
separating the first two cleavage-spheres half-larvae were
produced, but subsequent experiments made by Driesch
and Crampton have shown that these eggs resemble in this
respect those of many of the Echinoderms, for instance those
of a sea-urchin (Sphaerediinus). Interference with the cleavage-
cells and their isolation cause at first a defective cleavage,
producing only part of an embryo, but subsequently readjust-
ment sets in, and the part develops to a whole, so that finally
complete blastulae, gastrulae, and larvae are formed, but of
reduced size.
In the eggs of Ctenophora, Molluscs and many worms
there is only a very slight power of readjustment, and their
development appears as a mosaic work, but the eggs of the
bony fishes (Teleostei) and those of the famous Amphioxus
PKEFOBMATION OB EPIGENESIS ? 235
in regulatory power resemble those of the Echinoderms. There
is, however, in the eggs of the Amphioxus a certain tend-
ency to defective cleavage, i.e. to the formation of imperfect
embryos, and there is also a very rapid diminution in the
power of redifferentiation as the process of cleavage goes on.
In spite of this, however, at least in the early stages of
cleavage, dependent differentiation is far more apparent than
independent.
4. CONCLUSIONS
We have now completed our survey of the embryological
development of the eggs of various kinds of animals, and we
may pass on to the conclusions to be deduced from it. It will
tend to brevity and clearness if I present them in the form
of questions.
First : ' Is the ontogeny of the organism based upon
independent or dependent differentiation, on preformation
or epigenesis ? '
If we regard the fertilised ovum as a whole, then its em-
bryonic development from beginning to end is based upon
independent differentiation, and consequently upon preforma-
tion. But if, on the contrary, we take into account the relations
to one another of the individual parts of the egg and of the
embryo to be produced from it, the answer to the question is : —
Development is based partly on intrinsic, and partly on
extrinsic o^_dep_endent_^.fIerentiation.~Viewed as a whole,
the process of development appears to be an epigenetic evolu-
tion. Considered in detail, in the ontogeny of living organisms
dependent and independent differentiation act in many respects
conjointly, but in many other respects quite distinctly, not
only in the eggs of various animals, but in the stages of develop-
ment in the same embryo. Sometimes the development of
the parts of the embryo resembles a^ mosaic jwork, in which
each part takes its form irrespective of the other parts, as in
the Ctenophores. Sometimes it is more like a^harmonious
equi^otential system, in which each part is able to exchange
its role with every other part, or even to undertake the
duty of the whole, as in the sea-urchin blastula. In both
cases, however, the regular course of the various phases in
236 MODEEN BIOLOGY
development is controlled by the idea of the whole that is to
be produced, although in the latter case the idea is certainly
clearer and more definite than in the former.
We have seen that at the beginning of embryonic develop-
ment, the cleavage- cells of the embryo generally display a far
greater power of readjustment or redifferentiation than they
do later, and thus the prospective potency of the individual
cells is diminished the further the organs of the new creature
develop. From this point of view, development begins with
dependent differentiation and ends with intrinsic differentia-
tion of the various parts of the embryo.
Second : ' What connexion is there between the nuclear
substance of the egg^ell and the development of. the embryo ? '
This difficult question has already been discussed from the
standpoint of microscopical morphology in Chapter VI ; we
must now refer to it shortly on its embryological side. On
this subject there are two opinions current, in direct antagonism
to each other. According to one, supported chiefly by Wilhelm
Eoux and August Weismann, the chromatin nuclear substance
of the fertilised ovum and the cleavage-cells formed from it
exercises a controlling and regulating influence over the pro-
cesses of development By means of what Weismann calls
erbungleiche Teilung, or differential division, the chromosomes
of the cell-nuclei, which are the material bearers of heredity,
are distributed in different ways to the different cells of the
organism that is to be produced, and thus they determine the
character of the future tissues and organs. The other theory,
however, which is upheld chiefly by Oskar Hertwig l and Hans
Driesch, denies both the existence and the necessity of^any
differential division of the chromosomes. It recognises the
facts that they are to be regarded as material bearers of heredity,
and that they possess a certain amount of individual independ-
ence, but it does not ascribe to them so great a determining
importance in the processes of development as the former
theory assigns to them.
Both theories find support in significant facts, although
there are other facts which can hardly be reconciled with them.
The theory of differential division stands, perhaps, in more
logical connexion with the processes of karyokinesis that
1 Allgemeine Biologie, pp. 356, &c., 454, &c.
DIFFEKENTIAL DIVISION OF CHKOMOSOMES 237
have been observed under the microscope as taking place
during fertilisation. These show us not merely the regular
distribution of the chromatin substance of the nuclei of the
germ-cells to the daughter-cells of the embryo, but also a
division, which at least in many cases seems to be differential,
as the future germ-cells and the future somatic cells receive
remarkably unequal amounts of chromatin. Boveri and
other scientists have shown this to occur in the egg of the
maw-worm, Ascaris megalocephala var. bivalens, and Giardina
has observed it in that of the water-beetle, Dytiscus.1
The theory of differential division may find support also
in the embryological phenomena already described, in which
the development of the embryo is controlled chiefly by the
self-differentiation of its various parts, and therefore represents
a mosaic, as, for instance, in the Ctenophores. Moreover the
fact that, as the development of the embryo advances, the
prospective potency of its cells diminishes and becomes more
limited, can easily be explained by the theory of differential
division.
But against this theory and in favour of erbgleiche Teilung,
or integral division, there are many other facts in embryology
which have been carefully observed and are of no less signifi-
cance, the chief of them being that the single cells of the
embryo may form an equipotential system, the component
parts of which may be set to discharge the functions of any
other parts or even of the whole. When the sea-urchin egg is
in course of cleavage, each part of the blastula, cut haphazard
in any direction, is capable of becoming a complete blastula
able to develop further. This fact would seem to justify the
conclusion that the nuclear substances of the single cells in
the embryo are absolutely equivalent to one another, and
that consequently no differential division can have taken
place at the cleavage of the ovum. Against the theory of
differential division is the further fact that the development
of the special Anlagen for the future organs in the embryo
is based chiefly upon dependent differentiation, whilst self-
differentiation asserts itself more in subsequent stages. It
appears, therefore, that, if we leave out of consideration the
very early differentiation between germ-cells and somatic cells,
1 Of. p. 122 and fig. 23, p. 124 ; also p. 169.
238 MODERN BIOLOGY
as a rule only an integral division of the bearers of heredity
takes place at the beginning of embryonic development. It is
possible that future research will show us how to reconcile
these two theories of integral and differential division, but at
present they are involved in many difficulties, and it is not
easy to view them impartially.
Of far greater importance than this purely technical ques-
tion is another, which is concerned with the philosophical
solution of the problem of life, and must therefore be discussed
more fully.
Third : ' Dp mechanical causes suffice to afford a satisfac-
tory explanation of the processes of development, orjtnust
we accept aspecial " vital " law to account for them, — a law
goveTntngTEe^ chemico -physical factors of development, and
directing them to the formation of an organism capable of
living ? ' In other words : ' In attempting to offer a philo-
sophical account of the phenomena of embryonic development
must we profess ourselves adherents of the " machine theory "
or of vitalism ? '
Vitalism is as old as natural philosophy itself. It is well
known that the scholastic philosophers adopted special formal
principles (entelechies) as the actual essential forms of living
matter, in order to account for the phenomena of life.
This is the earliest kind of vitalism, but, at the beginning
of the nineteenth century, it had been more or less forgotten
in scientific circles. Liebig and other chfmm'ata thought that
they must assume the existence of a SDecialkind of vital force
working in living organisms, over and above mechanicaHorces.
Towards the end of the century neovitalism entered upon a
new stage, approximating to the vitalism of the old philo-
sophers. Two of the chief advocates of neovitalism, J. Reinke,
the botanist, and Hans Driesch, the zoologist, do not regard
the principle of life as a causa efficiens of the vital processes,
but as an internal formal principle of the living organism. We
shall recur to this topic later (cf. p. 243).
The machine theory was the outcome of the great success
with which the mechanical view of nature was applied to
physics and chemistry in the nineteenth century, but, when it
is closely examined, it is found to be based upon a one-sided
overvaluation of the importance of mechanics in explaining
VITALISM 239
natural phenomena, and it cannot hold its own against a
thorough criticism. It still has many adherents, for old
prejudices die hard. Professor Otto Biitschli defended it
against the supporters of-neovitalism at the fifth international
Zoological Congress at Berlin, and read a long paper entitled
* Mechanismus und Vitalismus ' on August 16, 1901. l In this
paper Biitschli remarks : ' The machine theory regards it as
possible, though for the moment only to a very limited extent,
to account for the forms and phenomena of life on the lines of
complex physico-chemical conditions. Vitalism, on the con-
trary, denies this possibility. The vitalist is convinced that
the physico-chemical action of inorganic nature is not sufficient
to account for organic life, that an altogether peculiar action,
unknown to inorganic nature, must exist in the world of organic
life.' Biitschli states the question clearly and accurately, but
unfortunately we cannot say as much for his arguments in
favour of the machine theory. I listened to what he said with
attention, and read a report of it afterwards still more atten-
tively, but I discovered only one real piece of evidence in favour
of the machine theory as an explanation of life, and this one
piece of evidence occurred in the closing words of his dis-
course : ' Of all the phenomena of life we can understand only
what admits of a physico-chemical explanation.'
Professor Biitschli will, I hope, forgive me for saying that
this kind of evidence seems to me quite unintelligible. If it
were accurate, the thoughts of the speaker would be pronounced
unintelligible for himself as well as for his hearers and readers.
According to his own opinion, his thoughts undoubtedly
belong to the category of phenomena of life. He ought,
therefore, first to give us a physico-chemical explanation of
his own process of thought, before he calls upon us to under-
stand his defence of the machine theory !
Biitschli was certainly arguing in a circle, and thus his
arguments had no logical force. He confused the ideas of
' to understand ' and ' to give a physico-chemical explanation,'
and regarded them as synonymous, but I must protest against
being required to accept this. Either he assumed that the
phenomena of life, considered scientifically, admitted only of
a physico-chemical explanation — which was exactly what he
1 See Verhandlungen, pp. 212-235.
240 MODEKN BIOLOGY
undertook to prove — or he did not assume it, and then he has
simply not given us the evidence to prove that the phenomena
of life have no special vital laws governing them, over and
above what is physical and chemical. It is time for people
to give up attempting to combat the vitalist theory with such
threadbare arguments.
In the interests of modern biology I must enter a further
protest against Butschli's entirely ungrounded assertion, that
we can understand only what admits of chernico-physical
explanation, and can understand it only as far as it can be
explained on these lines. If this were true, the scientific
value of the greatest biological triumphs of the present day
would be absolutely nothing. Are we in a position to give a
physico-chemical explanation of the processes of indirect
karyokinesis, of fertilisation, and of ontogeny ? Are they
therefore simply unintelligible to us ? No, they are not ;
for we understand these phenomena chiefly by considering
their purpose and not their mechanical cause. Just as we can
understand why a key of a particular shape can turn in a lock,
without needing to know by what mechanical process the key
and the lock have been made, so we can grasp the significance
in fertilisation and development of the processes involved in
karyokinesis, although we do not know their chemico-physical
causes. The assertion that the scientific intelligibility _of a
biological process is limited by the knowledge we possess of
its physico-chemical causes, is therefore false and misleading,
as well as materialistic. A reasonable explanation of biological
phenomena cannot be given, unless they are observed from
both the teleological and the causal, mechanical points of view,
since both are worthy of equal consideration.1
An opinion identical with my own was expressed by L.
Khumbler in an address delivered at the seventy-sixth meeting
of German naturalists and physicians at Breslau : ' The
mechanical processes of 'the cell do not exhaust the powers of
a living cell, but concern it only on its physico-mechanical
side.^
Other advocates of the machine theory have not been
1 On this subject see also J. Reinke, Philosophie der Botanik, 1905, chapter
iii, * Kausalitat und Finalitat ' ; also ' Neovitalismus und Finalitat in der
Biologic ' (Biolog. Zentralblatt, 1904, Nos. 18 and 19, pp. 577-601).
2 Naturwissenschaftliche Rundschau, 1904, Nos. 42 and 43, p. 549.
THE MACHINE THEOBY OB VITALISM ? 241
much more successful in adducing satisfactory evidence to
support it. Max Verworn, a famous physiologist, writes as
follows in the introduction to his ' Zeitschrift fur allgemeine
Physiologie' (Vol. I), when attacking neovitalism and defending
the machine theory : ' The principles of action must be the
same everywhere, as long as we move in a material world.'
But why ? Can this be decided at all a priori ? Must not
the question, whether the principles underlying inorganic and
organic action are identical or not, be answered by experience ?
Experience tells us that the vital processes are of such a kind
as not to admit of any purely mechanical explanation. There-
fore a vitalist is justified in saying : ' The vital processes are
governed by laws of their own, which are superior to chemico-
physical activity.' By his method of defending the machine
theory Verworn has really cut away the ground from under
his own feet. He asserts that purely mechanical principles
must be equally applicable to living and to lifeless bodies,
and he goes on to prove the truth of this assertion by saying
that ' physiology can never be anything but physics and
chemistry, i.e. the mechanics of the living body.' Therefore
physiology, as a special branch of biology, is quite superfluous ;
we may quietly let it drop, and incorporate it with physics and
chemistry — though perhaps Verworn, being one of our most
eminent physiologists, will hardly agree to this.
If physiology were to be nothing more than applied physics
and chemistry ; if the whole scientific value of physiology
were to be measured by its success in tracing all living action
back to chemico-physical causes, then indeed modern physio-
logy with its imposing achievements would be in a sad plight.
G. von Bunge says in his famous manual of human physiology
(' Lehrbuch der Physiologie des Menschen,' II, 1905, 3) : ' The
opponents of vitalism and adherents of the mechanical explana-
tion of life are accustomed to justify their views by maintaining
that, the further physiology advances, the more successful
are they in referring to physical and chemical laws those
phenomena which used to be ascribed to some mystical vital
force ; it is therefore now only a matter of time, and eventually
the whole vital process will appear to be a complicated set of
movements, governed solely by the forces of inanimate nature.
It seems to me, however, that the history of physiology teaches
242 MODEEN BIOLOGY
us the exact opposite, and I maintain that the supporters of
the machine theory are wrong. The more thoroughness,
acumen, and impartiality we bring to bear upon our examination
of the phenomena of life, the more do we perceive that
processes, for which we had thought it possible to account by
means of physics and chemistry, are of jifarmore complex
character, and for the present defy every^ attempt "to explain
them in a mechanical sense.' Bunge had previously declared
that the machine theory of the present day would inevitably
drive us towards the vitalism of the future, and he was quite
right. Oskar Hertwig uses similar language in his ' Allgemeine
Biologie' (1906), p. 551, where he says: ' The development
of the eye, the ear, and the larynx, as well as of the bones, has
hitherto not been explained on mechanical lines, in fact, we
may say the same of every process of development ; for every-
where we meet with a factor outside the scope of mechanical
knowledge, although it is the most important of all, and
this factor is the activity of the cell-organism.'
1 But,' say the champions of the machine theory, ' vitalism
directly contradicts the universally recognised law of mechani-
cal energy. If there were a special vital activity, it would
violate trie law of the conservation of a constant amount of
energy in the universe — and therefore we cannot accept
the theory of vitalism.' What answer can we give to this
argument ?
The law of energy in its original form is a purely mechanical
law, ancfcan trier eiore_a,ppAy only to the operation of mftpJiarii-
cal factors. It is applicable to psychical and vital factors
only in so far as they make use of mechanical agencies in doing
their own work, and no further. Whoever has recourse to
the law of energy in order to prove a psychical or vital action
impossible, is either silently assuming that all action in Jhe
universe must be essentially mechanical, — and then he is
taking for granted what it was his business to prove — or his
whole line of proof is useless.
^ The assumption of a special vital action would be really
contradictory to the law of energy only if the operation of the
vital principle either increased or diminished the fixed amount
ofmechanicalljriergy ; but this is a complete misrepresentation
of true vitalism. We need no old-fashioned ' vital force '
THE MACHINE THEOEY OK VITALISM ? 243
acting like a deus ex macJiina, pushing and pulling and inter-
fering with mechanical factors, but we require a vital principle,
which as causa formalis enables the atoms and molecules of trie
living body to accomplish their chemico-physical tasks with a
definite vital aim. All the mechanical work performed may
be put down exclusively to the chemico-physical factors, and
not to the vital principle, therefore it is impossible for the
latter to violate the law of the conservation of energy.
The only correct view of the laws of life, which constitute the
essential difference between living organisms and inorganic
natural bodies, was stated centuries ago by the Aristotelian
philosophers (see p. 238), and has recently been adopted by
eminent naturalists of our own day.1 Especial mention
must be made of Hans Driesch,3 a great embryologist, who
has declared himself a supporter of the ' Autonomy of the
Vital Processes,' and has lately expressly described the vital
or formal principle, as one corresponding to Aristotle's
entelechies.
J. Beinke, the well-known botanist, speaks of dominants, j
which are closely akin to the idea of entelechies.3 These state- !
ments may suffice to weaken the objections raised against
vitalism by the upholders of the machine theory, and, on the
other hand, to give a correct idea of what vitalism really is.
If we are now asked the question whether the assumption
of a special vital law, controlling the chemico-physical agencies,
is absolutely necessary, in order to supply a reasonable explana-
tion of the embryological processes described in this section,
we may answer shortly : * The assumption of a vital principle
is absolutely necessary in order to account for the phenomena
of development.'""
I have already alluded to the inadequacy of the attempts
made by J. Loeb and others to explain the cleavage process of
1 On this subject see Hans Malfatti, ' t)ber die Chemie des Lebens ' (Die
Kultur, 1905, Part I, pp. 41-49).
2 Ergebnisse der neueren Lebens forschung, 14 ; see also by the same author,
Organische Regulationen, Leipzig, 1901, and Die Seek als elementarer Naturfaktor,
Leipzig, 1903.
3 Die Welt als Tat, Berlin, 1903, pp. 275-292 ; Einleitung in die theoretische
Biologie, Berlin, 1901, chapters 19 and 20. 'Die Dominantenlehre ' (Natur
und Schule, 1903, Parts 6 and 7). See also Reinke's more recent work, 'Der
Neovitalismus und die Finalitat in der Biologie ' (Biolog. Zentralblatt, XXIV,
1904, Nos. 18 and 19, pp. 577-601) ; also Philosophie der Botanik, 1905,
chapter iv.
B 2
244 MODERN BIOLOGY
the ovum on purely mechanical lines (see p. 222), I have
referred to dependent differentiation and to redifferentiation
or readjustment as facts supporting the theory of epigenesis,
and have shown in several places (pp. 229, 230, &c., and 235),
that we can account for these facts only if the whole process
of development is dominated by the idea of the whole that is
to be produced — a form of expression frequently used by
Korschelt and Heider in their excellent * Lehrbuch der vergleich-
enden Entwicklungsgeschichte.'
We cannot dispense with a teleological interpretation of
the processes of development ; they are absolutely incom-
prehensible, unless we assume the existence of a formal principle
controlling the mechanical agencies, and directing them to
the aim of producing an organism capable of life.
But is it altogether impossible to regard the fertilised ovum
from the point of view of the preformation theory, as a wonder-
fully delicate and complicated machine, set in motion by
purely mechanical agencies and effecting the regular con-
struction of the organism in the process of development ?
This machine theory of life -was once upheld by Hans Driesch,
but he has recently subjected it to a very searching criticism
and condemned it as quite untenable. In his ' Ergebnisse der
neueren Lebensforschung' (p. 15), he writes : ' Eggs are the result
of an extremely complicated formative process ; therefore
each egg might be considered as a very complex piece of
machinery, though so small as to be invisible to the naked eye.
Now in the course of the ontogeny of an individual, all the
eggs have been formed from one cell, by division. How can
a complex piece of machinery go on dividing and yet remain
complete ? It is impossible, and therefore, in this department
also, the machine theory breaks down.'
In fact a machine, at once so delicate and so ingeniously
constructed, able spontaneously to divide itself a hundred
times, and yet to preserve in all its parts the power to become
a complete machine again automatically, would be so wonderful
a piece of mechanism as to be absolutely inconceivable.
The machine theory of life breaks down in the equipotential
systems (see p. 227) no less than in the development of the
ovum. Let us refer to a statement made on p. 231 with regard
to the blastula of the sea-urchin egg. Such a blastula may be
DKIESCH ON THE MACHINE THEOKY 245
cut up in any direction, and each piece will grow into a complete
blastula ; in fact every one of the 808 cells forming the
blastula is capable of exchanging its original function with any
other cell of the same blastula. Now imagine a machine consist-
ing of 808 parts ; hack the machine to pieces, and see if each
single piece is able ' by means of physico-chemical factors ' to
complete itself automatically, and produce a whole machine
able to work. A machine, capable of doing this, is again
something absolutely inconceivable.
I may quote from Driesch l another classical instance
showing that the machine theory of life is absolutely untenable.
He made a series of experiments on an Ascidian, Clavellina
, a rather highly organised creature, which he
describes as follows : ' Clavellina is about an inch long, and
its body consists of three chief parts ; at the top is an
extremely large, basket-shaped branchial sac, with openings
for water to flow in and out ; in the middle is a slender portion
of the body, which contains the stomodseum and proctodaeum,
and behind it we see the intestinal sac, containing the stomach,
intestine, heart, organs of propagation, &c.
' If- a Clavellina is cut in two, across the narrow part of its
body, so that the branchial and the intestinal sacs are separated,
each of these two parts is able in three or four days to grow
into a complete animal, as, by means of regeneration from the
wounded surface, the branchial sac supplies itself with an
intestinal sac, and the intestinal sac with a branchial sac.
But the branchial sacs of Clavellina do not, when isolated,
always behave in the way just described. About half of them,
and especially those belonging to small specimens, arrive at
the formation of a new whole, but by a totally different method.
They do not begin by producing any new formation at all, but
they undergo a complete transformation. The organisation
of the branchial sac, its ciliated stigmata, apertures, &c.,
gradually vanish, and after five or six days it is no longer pos-
sible to trace any organisation at all, the creatures look like
uniform white balls ; in fact, when I first saw these shapeless
1 * Studien iiber das Kegulationsvermogen der Organismen ' : 6. ' Die
Restitutionen der Clavellina lepadiformis ' (Archiv /. Entwicklungsmechanik,
XIV, 1902, Parts 1 and 2, pp. 247-287) ; see also Ergebnisse der neueren Lebens-
forschung, pp. 10-12.
246 MODEKN BIOLOGY
masses before me, I thought they were dying, if not actually
dead. But such is not the case. They may remain for as
long as two or three weeks in this shapeless condition ; then,
one day, they begin to show signs of life and to stretch, and
in two or three more days they are again complete Ascidians,
with branchial sac, intestinal sac, &c. They are absolutely
new creatures, having no part in common with the original,
but made of the same material. Their branchial sacs are not
the old ones that were cut off, but are much smaller, with
fewer channels, and fewer and smaller apertures.
' The organisation of the isolated branchial sac seems to
have been reduced to undifferentiated material, out of which,
as in embryonic development, a complete little organism has
been formed. Sections made by the microtome through the
balls undergoing retrogressive transformation show that the
change of differentiated into undifferentiated substance had
gone very far. We now come to the most important point
in the results of our experiments on isolated branchial sacs
of Clavellina. Not only is the isolated branchial sac itself able
to become a little Ascidian by means of retrogressive trans-
formation and regeneration, but it may be cut in half in any
direction, so as to form an upper and a lower, or a front and
a back half, and each half still possesses the power to undergo
retrogressive transformation, and to develop into a little
Ascidian, complete in every detail of its organisation. This
is undoubtedly an extremely strange phenomenon in organic
formation.'
So far I have quoted from Driesch. Let us now compare
the capacity of reformation possessed by the branchial sacs or
portions of them, undergoing retrogressive transformation,
with the favourite example of a machine of very complex
structure, such as the upholders of the machine theory regard
as essentially equivalent to a living organism. Let us imagine
that we break the machine in pieces, and choose one piece,
which we break again, for closer observation. After a few days
this piece falls into a confused mass of fragments, so that
nothing of the original parts of the machine can be recognised.
It remains in this condition for some weeks, and then suddenly
begins to move, the various bits of iron come together quite
spontaneously and form, not the original piece of the machine
VITALISM ALONE ACCEPTABLE 247
which gave rise to the mass of fragments, but a new and
complete little machine, constructed on the same lines as the old
one. Any one would say that nothing short of witchcraft could
accomplish this, and it is a fact that a Clavellina, acting in
accordance with the machine theory of life, would never
naturally succeed in performing such a feat. We declare,
therefore, that the machine theory, which, in spite of the
accomplishment of such wonders, persists in regarding the
Clavellina as a mere machine, makes large demands upon our
credulity. But as we are convinced that natural causes, and
not magic arts, underlie the marvels of development, we come
to this conclusion : Vitalism is the only philosophical theory
of life that is in accordance with reason, for it d.oes not regard
the livingorganism as a mere machine, but it knows howjfcp
find the architect residing in it !
1 In the smallest cell we have all the problems of life before
us.' These words of Bunge's l have found abundant confirma-
tion in the preceding pages. A diminutive egg-cell, once
fertilised, contains already the design of the whole complex
organism which is to proceed from it, and it contains it in a
way that defies all purely mechanical explanationT The study
of ontogeny has brought us to the same conclusions as those
which we expressed at the end of Chapter VI (pp. 177, &c.),
although by another road, that, namely, of modern embryology.
In Chapter VI, the results of microscopical study of the
phenomena of fertilisation and heredity led us to assume
the existence of internal laws of development, controlling the
maturation-divisions of the germ-cells and their union in
the course of fertilisation, and directing these processes to
a definite end. We found that the chromosomes should
probably be regarded as the chief material bearers of heredity,
but their morphological function was by no means a satis-
factory explanation of the real problem of development. Even
if the supporters of the chromosome theory really succeeded,
by means of most accurate microscopical observations, in
showing conclusively that their theory agreed with the results
of embryological physiology ; even if they were able to
express the amazing processes of regeneration in Clavellina by
1 Lehrbuch der'.Physiologie des Menschen, II, 11.
248 MODEBN BIOLOGY
a complicated formula of chromosomes (which would have
to surpass in ingenuity the System of the Universe, the out-
come of Laplace's giant intellect) — they would still not have
solved the mystery of life, as it is presented to us by the problem
of ontogeny. The external aspect of the problem, and no
other, can be dealt with by means of microscopical observation,
and by considering the morphological peculiarities of chromo-
somes of definite shape, dividing in definite ways, and distri-
buting themselves in definite numbers to the various cells
of the new organism — we have still not touched the other side
of these embryological processes, which is concerned with
their interior dynamics. The physiological part played in
the maturation and fertilisation of the germ-cells, and in the
subsequent cleavage-divisions of the embryo, by the 'chromo-
somes, as bearers of heredity, upon one another and upon the
cell -plasm, goes far beyond the scope of the most subtle machine
theory, and reaches far into the domain of the mysterious
conformity to vital laws that manifests itself in living creatures.
In studying the processes both of fertilisation and of develop-
ment, we must necessarily assume the existence of some inner
causes working harmoniously to one common end, and thus
only shall we understand the physiological importance of the
chromosomes. If, on the one hand, these material parts,
visible only under the microscope, are really the smallest
wheels, setting the wonderful clockwork of life in action from
generation to generation, and if the movements of these wheels
are due immediately to some still unknown chemico-physical
laws acting upon the molecules of albumen and nuclein in
the cells, we must remember that, on the other hand, they
are living wheels, and it is only from their uniform action,
which has the whole vital process as its aim, that the chromo-
some theory of the future will ever be able to supply a really
satisfactory explanation of the phenomena of life. This
uniform action, however, must have a uniform interior cause,
and this we perceive in the vital principle of the organism
to which I have already alluded.
In Chapter VII we considered a number of facts, that led
us to accept this immanent teleological principle, whilst they
revealed the impossibility of spontaneous generation. Now
that we have surveyed the results of modern embryology, the
VITALISM ALONE ACCEPTABLE 249
acceptance of this same principle has been shown to be necessary
in a far higher degree.
The vital^rincjple, that controls what goes on in a diminu-
tive fertilised ovum, is at the same time the architect, directing
the course of the whole resulting process of development, and
bringing it to completion by means of the mechanical agencies
that are subordinate to him. But this little architect is not
himself an intelligent being ; he has power to act in the various
cells and in the whole organism, and to direct all to their aim,
but he does so in virtue of the laws which a higher intelligence,
superior to our universe, imposed upon living matter when the
first organisms came into being. This higher intelligence we
call a personal Creator. The necessity for assuming the
existence of this first cause for all conformity to law in organic
life — would remain undiminish^HT if f.he machine' theorists
succeeded in accountiri^ for all the vital process^ without, a.
vitai ' principle. Only an architect of infinite intelligence
could possibly construct a machine capable of developing,
growing, and propagating itself for millions of years by means
of purely mechanical agencies. The reasons for regarding the
machine theory of life as untenable are therefore not theological,
but scientific. Unicellular living creatures and the fertilised
ovum and the organism proceeding from it, all have in them-
selves the vital principles, which uniformly direct the action
of the chemico-physical forces of the single atoms towards the
higher aim of life.
Our praise is due, not to these diminutive, unconscious
architects, but to the eternal creative Spirit that has con- .
nected them with matter.
CHAPTEE IX
THOUGHTS ON EVOLUTION *
1. THE PROBLEM OF PHYLOGENY.
Its hypothetical character (p. 253). Evidence in favour of race-evolu-
tion (p. 254). Positive scientific evidence is all in favour of
polyphyletic evolution (p. 255).
2. THE VARIOUS MEANINGS OF THE WORD 'DARWINISM.'
Fourfold use of the name (p. 257). What view must we take of Dar-
winism ? Darwin's theory of selection is not the whole of the doctrine
of evolution (p. 259). Haeckel's testimony to this fact (p. 261).
Nee-Darwinism and Neo-Lamarckism (p. 263). The Darwinian
cosmogony (Haeckelism) is wrong (p. 265). Equally wrong is its
application to man (p. 266).
3. THE SUBJECT OF THE DOCTRINE OF EVOLUTION AS A SCIENTIFIC THEORY.
It is not concerned with the origin of life (p. 268). Its task is to investi-
gate the facts and causes connected with the different series of
organic forms (p. 270).
4. THE THEORY OF EVOLUTION CONSIDERED IN THE LIGHT OF THE COPER-
NICAN THEORY OF THE UNIVERSE.
Kant and Laplace's theories regarding the development of the celestial
bodies. The geological formation of our earth and its natural
causes (p. 273). The sequence of species of plants and animals
in the course of the history of our earth is to be explained by
natural causes, i.e. by evolution, not by repeated acts of creation
(p. 275). Instances from palaeontology (p. 276).
5. PHILOSOPHICAL AND SCIENTIFIC LIMITATIONS OF THE THEORY OF EVOLUTION.
First : Philosophical limitations (p. 279). Recognition of a personal
Creator. His action regarding the origin of primitive organisms,
their number and mode of evolution being unknown to us (p. 280).
A creative act is indispensable to account for the mind of man (p. 283).
Second: Scientific limitations (p. 285). Hypothesis and theory.
Theories of permanence and descent (p. 285). When did the
first organisms come into being ? (p. 288). Monophyletic or
polyphyletic evolution ? (p. 291). The causes of race -evolution
(p. 294). Problems still to be solved relating to the course and
causes of race evolution (p. 295).
6. SYSTEMATIC AND NATURAL SPECIES.
The natural species is a series of forms of systematic species genetically
connected (p. 296). Scientific and philosophical importance of the
distinction between natural and systematic species (p. 297). The
theory of evolution is perfectly compatible with the dogma of creation
(p. 299).
7. SUMMARY OF RESULTS.
1 An article published in the Biologisches Zentralblatt for 1891 (Nos. 22, 23),
dealing with the evolution of the varieties of Dinarda, gave rise to a number
of unfair remarks upon my attitude towards the theory of evolution. I thought
it possible to show that the varieties of the Dinarda beetle, living among our
250
THOUGHTS ON EVOLUTION 251
1. THE PROBLEM OF PHYLOGENY
THE ontogeny of organisms, which we discussed in the
previous chapter, is a direct object of scientific observation.
That the seed of a rose develops into a rosebush, and a hen's
ants, were not strictly speaking species at all, but races, standing on various
levels with regard to the formation of species. Further, I was able to show that
the differences in our various kinds of Dinarda appeared to be characteristics due
to adaptation of their way of life to that of the various kinds of ants who were
their hosts. In this article I mentioned shortly several other facts, that I
had observed in the course of my special study of the inquilines among ants
and termites, and that I considered were arguments in favour of a modified
theory of evolution. I remarked emphatically that I regarded the theory as
justified only in so far as it is really based on ascertained facts in the case of
definite series of forms ; I altogether refused to accept the so-called ' Postu-
lates,' which the monists set up in the name of the theory of evolution.
In spite of this important reservation, a reviewer in the Schlesische Zeitung
of January 21, 1902, ventured to claim me simply as a supporter of the theory
of descent. In the Supplement to the Allgemeine Zeitung for June 17, 1902
(No. 136), a longer article appeared by Dr. K. Escherich, entitled, 'A Jesuit as
an adherent of the theory of descent.' It is true that my own opinions were
reproduced in it with praiseworthy accuracy, and that attention was drawn
explicitly to my not regarding as justifiable the extension of the theory of
evolution to man. But the reviewer went on to express a hope that the
theory would soon be accepted without reservation by me and the whole
Catholic Church ! I think, therefore, that I am absolutely bound in this
place to state clearly what I am ready to accept in the theory of evolution,
and what I reject as mere additions from Darwinian and monistic sources.
Moreover, in his review Dr. Escherich spoke of me as an opponent of the other
advocates of the Christian cosmogony, and especially of all other Catholic
theologians, and this is certainly not the truth. It is not a dogma that every
species owes its existence to a particular act of creation. More than twenty-
five years ago Father Knabenbauer. S.J.. contributed a very careful article
on * Glaube und Deszendenztheorie ' (' Faith and the Theory of Descent')
to Stimmen aus Maria-Loach (XIII, 1877). On p. 72 of this article he says :
* Faith does not forbid us to assume Trial the now existing varieties of plants
and animals are derived from some few original forms.' Professor Schanz
expresses similar views in his Apologie des Christentums, 1895, to which attention
was drawn by articles in the supplement to the Germania, July 3, 1902,
No. 150, and the Deutsche Eeichszeitung, No. 326. More than twenty years ago,
the Stimmen aus Maria-Loach several times contained emphatic warnings to
be careful to distinguish Darwinism and the theory of evolution; although
the former must be rejected, there are many facts to support the theory that
organic species have developed within definite series of forms.
Extracts from Escherich's review concerning my attitude towards the
theory of descent were subsequently reprinted in the Frankfurter Zeitung of
July 18, 1902, No. 197 ; in the Deutsche Zeitung, No. 168 ; and in the Bohemia
of July 20, No. 198 ; with the unfortunate title ' Ein Jesuit als Anhanger des
Darwinismus ' (' A Jesuit as an adherent of Darwinism '). In order to remove
all misunderstandings that may have arisen in consequence of these newspaper
reports, I intend to make a clear and detailed statement here of my opinions
on the subject of evolution, which have also been expressed in a number
of lectures of a popular scientific nature, delivered in various German towns
and in Luxemburg since the year 1901. It was easy to foresee that the extreme
Darwinists would attack my views, but I can notice only those attacks which
have some foundation on facts. Further remarks on this subject will be
found at the beginning of this book in the ' Few Words to my Critics/ and
at the end, in the appendix containing my Innsbruck lectures.
252 MODEBN BIOLOGY
egg into a chicken, are facts of everyday occurrence. Therefore
the study of individual ontogeny, which concerns itself with the
way in which the various living organisms of the present day
come into being, is in its nature an empirical science. In it
hypotheses and theories begin only at the point where we
seek a deeper insight into the laws and causes of the actual
development which we can observe.
But with the race history of organisms it is otherwise.
The science dealing with this subject is generally called simply
the doctrine of evolution or the theory of descent. It is not
empirical, but by its very nature it is a hypothesis, which
has grown into a theory by the aid of the circumstantial
evidence adduced in its support. I propose to do my best to
give my readers a clear idea of what it implies.
Hoses and poultry have not always existed, both in fact are
of very recent date ; the earliest representatives of the family
to which our poultry belong are found in the upper Eocene, i.e.
in the Tertiary period of the earth's history. Whence came the
first rose, and the first hen ? Were they suddenly created, just
as we know them, or were they developed from other kinds of
plants and animals that lived before them ? If so, how was
this development or evolution effected ? These questions are
very simple and obvious, and yet they are of great importance
in our comprehension of the vegetable and animal world
about us. The Flora which now covers the face of the earth
with leaves and blossoms, and the Fauna which now under
various forms inhabits sea and land, are not the original occu-
pants of our world, but late-born epigoni. They took the place
of other plants and animals which lived in the same world
before them, and are to some extent known to us through their
fossil remains ; and these earlier plants and animals had other
predecessors in still more remote periods, and so we may go on,
until at last we come to the first and oldest forms of animal
and vegetable life on our planet. And here again the same
question confronts us : ' Did the later representatives of the
Flora and Fauna come into existence quite independently of
the earlier ones, or are they chiefly their modified descendants ? '
We know that geology divides our earth into a series of
strata, formed successively one after the other, and arranged
one above the other.
THE PEOBLEM OF PHYLOGENY 253
I. Azoic or archaic strata, containing no organic remains.
II. Palaeozoic strata, containing the earliest traces of
organic life —
1. Cambrian (including Pre-Cambrian). •
2. Silurian.
3. Devonian.
4. Carboniferous (Coal).
5. Permian (Dyas).
III. Mesozoic strata (the middle ages of organic life) —
1. Triassic (red sandstone, shell lime, marl).
2. Jurassic (black, brown, and white Jura or Lias ;
Middle Jurassic or Dogger ; Upper Jurassic or
Malm).
3. Cretaceous (Chalk).
IV. Caenozoic strata (the modem period of organic life) —
1. Tertiary age (Eocene, Oligocene, Miocene, Pliocene).
2. Quaternary age (Pleistocene or Diluvium, Present
or Alluvium).
Man, the highest of all created beings, appeared only in the
Pleistocene period ; but the history of animal and vegetable
life upon earth began thousands, perhaps millions of years
before man's appearance. No human eye beheld the beginning
of the drama of life on our planet, no human eye watched the
thousands of scenes enacted from the moment when the great
drama opened, to the moment when man came forth as the last
and noblest figure on the stage of life. And now he ventures
boldly to look back into the past and survey the whole history
of the evolution of organic life on earth. He tries to find out
in what order the various forms of animals and plants have
succeeded one another, from the earliest times down to the
present day, and he attempts to account for this succession
by tracing the later forms back to the earlier, by means of
natural evolution of species, genera, families, &c.
It is therefore quite intelligible that this theory of evolution,
having as its subject the conjectural race-history of the organic
world, cannot be an empirical science, but bears, and must
inevitably bear, a hypothetical character. But as the human
spirit of research makes use of facts as a starting point for its
comparisons and deductions, the theory of evolution rightly
claims to be called a science, scientia rerum ex causis ; for
254 MODEEN BIOLOGY
race-evolution, if we accept it, enables us to give a comparatively
simple and natural explanation of a number of phenomena
actually occurring in various departments of biology. Inas-
much as it is in a position to offer the most probable account
of these facts, we must undoubtedly regard the theory of
evolution as scientific, although the evidence which the scientist
can use in support of the theory is almost exclusively circum-
stantial ; and indeed we cannot expect it to be otherwise,
for we are dealing with the previous history of the living
organisms known to us, with a primaeval period, of which at the
present day we find only faint traces and fragmentary remains.
Like a skilful advocate, the man of science must carefully
collect his circumstantial evidence, and fit it together, so as to
reconstruct from it a course of events which no one actually
witnessed.
The circumstantial evidence in support of race-evolution
is of many different kinds. It consists firstly of the facts of
palaeontology, which offers us the fossil remains of extinct
animals and plants as silent witnesses to the primaeval history
of our present Fauna and Flora. We have also the facts of
variation and mutation, which show us how the properties
of still existing creatures can be modified, and new species
formed. Comparative bionomics shows us how animals and
plants undergo adaptation to one another, and are influenced
by very various external factors, and these facts enable us
to infer how the altered relations have come about. The
facts of comparative morphology also, the points of likeness
in interior and exterior structure that exist among members
of definite families, these too are quite explicable if we may
assume that they have a common descent. Lastly, there are
the facts concerned in the ontogeny of the individual, which
incidentally reveals to us traces of former race-evolution.
In short, the various branches of zoology and botany — both
empirical sciences — supply innumerable pieces of circum-
stantial evidence, of which the theory of descent makes use.
If it does so in a critical and careful manner, we have a scientific
foundation for the theory of evolution, although we have no
wish to deny its hypothetical character. If, however, the
circumstantial evidence is used in a superficial and fanciful
way, and involves groundless generalisations and reckless
THE THEOKY OF EVOLUTION 255
jumping at conclusions, we have, instead of a scientific theory of
evolution, merely a fantastic semblance of it, which is pre-
tentious enough to put forward its arbitrary statements as
historical truths.
The very subject-matter of the theory of evolution shows —
and I am careful to emphasise it again — that it is indeed based
upon many results of the empirical sciences, but can never
be itself an empirical science, and will always remain a hypo-
thetical explanation of observed facts, and as such it has risen
to the rank of a theory. We must, however, always be careful
to distinguish hypotheses and facts ; and this is especially
necessary, because the theory of evolution in many respects
stretches beyond the domain of natural science into that
of natural philosophy, and it is often difficult to define the
boundaries of each. For this reason we must act cautiously
with regard to the * postulates ' which so-called monism
has set up in the name of the theory of evolution, for
they are not based on scientific facts, but on materialistic
dogmas.
Without entering upon a full account of the history of the
theory of evolution, I may shortly sketch the outlines of the
problem with which we are going to deal.
In order to explain the origin of the existing species of
plants and animals, we have to assume one of two things. We /
may assume that the systematic species (e.g. lion, tiger, polar
bear) are invariable — apart from the formation of varieties
and breeds within the species — and that they were created
originally in their present form. Or we may assume that 2.
the systematic species are variable, and constitute definite
lines of descent, within which an evolution of species has taken
place during the geological periods. The first of these assump-
tions belongs to the theory of permanence, the second to the
theory of evolution or descent. In the latter we must make
a further distinction between monophyletic and polyphyletic
evolution. According to the monophyletic theory, all organ-
isms have originated in one single primitive cell, or perhaps there
is one pedigree for all animals and one for all plants, each
having one primitive ancestor. According to the polyphyletic
theory there are several pedigrees for both plants and animals,
independent of one another, but each one going back to one
256 MODEEN BIOLOGY
special primitive form as its starting point.1 In the following
pages we shall see that the latter assumption alone can claim
to have any positive scientific probability — and we shall see,
moreover, that this assumption is perfectly reconcilable with
the Christian doctrine of the Creation.
2. THE VARIOUS MEANINGS OF THE WORD ' DARWINISM '
For over forty years a conflict has been raging in the in-
tellectual world, which both sides have maintained with great
vehemence and energy. The war-cry on one side is * Evolution
of Species,' on the other ' Permanence of Species.' No one
could fail to be reminded of that other great intellectual
warfare regarding the Ptolemaic and the Copernican systems,
which began about three hundred and fifty years ago, and
raged with varying success for over a century, until finally
the latter prevailed. Perhaps the present conflict between the
theories of evolution and permanence only marks a fresh stage
in that great strife, and, if so, how will it finally be decided ?
The contest that we have to consider was stirred up by
Charles Darwin, when he published his book on the ' Origin
of Species ' about the middle of last century. The theories
advanced by Lamarck and Geoffroy St. Hilaire at the end
of the eighteenth and the beginning of the nineteenth centuries
may be regarded as causing preliminary skirmishes, but
Cuvier's powerful attacks soon succeeded in overthrowing the
new ideas of evolution (see p. 28). It was not until the
year 1859 2 that the great battle began, which has received
its name from the commander-in-chief of the attacking army,
Charles Darwin. The warfare with which we are now con-
cerned centres round Darwinism, so-called.
I say, so-called Darwinism. A few words of explanation
are absolutely necessary. The thick smoke of the powder,
which hid the battlefield from our gaze, is gradually dispersing,
1 It is of secondary importance to consider how many individuals there
were of each primitive form. The chief point is that the Anlage for evolution
in each primitive form differed from those of the primitive forms of other
lines of descent.
2 The first English edition of Origin of Species was published in November
1859, as Darwin himself stated, although 1858 is sometimes erroneously given
as the date of its publication. See Francis Darwin, Life and Letters of Charles
Darwin, I (London, 1888), p. 84.
WHAT IS DARWINISM? 257
and it is much easier now than it was twenty or thirty years
ago to survey the armies on both sides and to judge of their
positions, their strength and their mode of fighting, and to
value rightly what they have achieved and 'what they still
have to accomplish. It now appears that the number of
scientific combatants gathered under Darwin's banner is
still comparatively small. By far the greater number of
supporters of what was once called Darwinism are now ranged
under the standard of the theory of evolution, and no longer
under that of Darwinism. These troops form the rank and
file, but Ernst Haeckel is the leader of a corps of free-lances
and freebooters, conspicuous for the disturbance that they
cause in the name of ' Science.' l
Their weapons are not, however, of the best and noblest
sort, and their aim is not the triumph of truth, but rather the
plunder of the Christian camp, that they suspect to be situated
somewhere in the rear of their opponents' position. But victory
does not incline to them ; with their wooden swords they
bring upon themselves one defeat after another, and only
succeed in hindering the triumph of the picked troops of really
scientific men, who fight with better weapons on the side of the
theory of evolution.
It is time, however, to explain in simple words the simile
of the battle which has presented itself to our sight.
If we want to answer the question : 'What are WQ to think
about Darwinism ? ' we must first of all try to grasp clearly
the different senses in which this name is used.
The first and most obvious way in which the word Darwinism f
is used, is to designate the theory of selection, put forward by
Charles Darwin ; i.e. the special form of the theory of descent,
which traces back the evolution of organic species to natural
selection, as its chief, if not its only cause. Man uses his
intelligence to produce artificial breeds of domestic animals,
by selecting for breeding those that show the peculiarities
that answer his purpose. Darwin, however, assumes the
occurrence of a natural selection with no purpose at all ; he
thinks that, by its means, in the struggle for existence some
varieties prove better able to hold their own than others, and
1 On January 11, 1906, they founded the ' German Monistic League '
(Deutscher Monistenbund) in Jena, under Haeckel's presidency.
258 MODEEN BIOLOGY
their peculiarities are accentuated by transmission to following
generations, whereas the varieties that are less capable of
self-preservation die out. This is the fundamental idea of
Darwin's theory of selection.
The word Darwinism received a second meaning when it
was applied to an extension of the theory of selection to a new
and, as it was called, philosophical theory of the universe. It
was assumed that not only the organic species, but the whole
orderly arrangement of the world, had arisen out of an originally
lawless chaos by means of accidental ' Survival of the Fittest/
In Germany Ernst Haeckel has been the chief founder and
champion of this Darwinian theory of the universe, and there-
fore it is also known as Haeckelism. It bears the misleading
name of ' Realistic Monism,' but it would be better designated
' Materialistic Atheism.'
The third use of the word Darwinism proceeded from the
extension to man of Darwin's theory of selection. In this
sense, the theory that man is descended from beasts is called
Darwinism, whether it be Vogt's theory of the descent of man
from apes, or some more modern opinion of the same kind.
According to this ' Darwinian ' view of man, he is in both
body and soul nothing but a beast, that has accidentally
reached a higher point of development than his fellows. The
first to deduce this conclusion from the Darwinian System
was an Englishman, Huxley, in his work ' Evidence as to
Man's Place in Nature ' (London, 1863). He was followed by
Haeckel in his ' Natiirliche Schopfungsgeschichte ' (1868).
It was not until 1871 that Darwin himself made up his
mind to extend his theory to man in his ' Descent of Man.'
This book is really the weakest of all Darwin's scientific works.
In 1887 Wiedersheim attempted to give a detailed anatomi-
cal foundation for the descent of man from apes in his book
on the structure of man as evidence of his past (' Der Bau
des Menschen als Zeugnis fur seine Vergangenheit,' 3rd ed.,
Tubingen, 1902). An excellent refutation of this piece of
fiction was given in 1892 by 0. Hamann in an article on 'Darwin-
ism and the Theory of Evolution ' (' Darwinismus und Entwick-
lungslehre') (see p. 108, &c.). The weakness of the Darwinian
methods of proof is thoroughly displayed by J. Eanke in his
work on Man (' Der Mensch/ 2 vols.).
WHAT IS DAEWINISM? 259
The fourth and last meaning attached to the name Darwin-
ism is due to its having been applied first to a particular
form of the theory of descent, and afterwards transferred to
the theory of descent in general. Although this use depends
upon a confusion of ideas, the name is still in popular language
applied to the whole doctrine of the evolution of organic
species, as opposed to the theory of permanence, which assumes
that the systematic species never change, and were created
originally in their present form. In this sense, therefore, every
student of nature, who declares the species in any one genus
of animals or plants to be related to one another, is a Darwinist,
though erroneously so-called.
This last application of the name Darwinism ought to be
given up, as it only leads to confusion. It is based — and I
must again emphasise the fact — upon a logical blunder, for it
confuses the theory of evolution as a whole with a particular
form of it. This blunder was pardonable forty years ago, when
Darwin's theory of evolution was the only one known, but it is
pardonable no longer. At the present day it is unfair to
identify the ideas conveyed by the names * Darwinism ' and
* Theory of Evolution,' and it is done only with a special
intention ; the adherents of Darwinism, on the one hand, have
recourse to this device in order to propagate their obsolete
theory in popular circles, and the opponents of the theory of
evolution, on the other hand, try to annihilate every attempt
to question the permanence of species, by hurling at it the
epithet * Darwinism.'
It will now be an easier task for us to answer the question :
* What are we to think about Darwinism ? ' We see that the
question resolves itself into four.
1. What are we to think of Darwin's Theory of Selection ?
2. What are we to think of the extension of Darwin's
Theory of Selection, so as to make of it a realistic
and monistic theory of life ?
3. What are we to think of the application to man of
Darwin's Theory of Selection ?
4. What are we to think of the Theory of Evolution as
opposed to that of Permanence ?
It is the object of our present discussion to supply an
answer to the last of these questions, and I can deal with
s 2
I
260 MODEEN BIOLOGY
the first three only briefly, for they have often been answered
before, and admit also of much shorter answers than the fourth.
First. — Modern science can hardly be said to take into
account Darwin's theory of selection as the exclusive form
of the theory of evolution. It is full of weak spots, to which
attention was drawn as early as 1874 by Albert Wigand,1
and it is impossible any longer to avoid recognising them.
In the first place the theory of selection is in principle not
satisfactory, for natural selection may be able to .destroy
what is inexpedient, but not to produce what is expedient.
Therefore it simply leaves to chance the origin of advantageous
modifications, which lead to the formation of new species. A
theory based on chance is worthless as affording an explanation
y ^ oi conformity to law in nature. In the second place, most of
t^ie__variatiQns which serve as the groundwork of classifica/ETon
are biologically indifferent, and do not affect the individual
or the species in the struggle for existence ; they can therefore
not be due to natural selection in their breeding, because they
(7 ^ present no points d'appui on which it can work. In the third
place, in order to account for the formation of one new species,
this theory requires innumerable, almost imperceptible varia-
tions to have existed for immense periods of time and to have
been gradually accumulating and intensifying. This con-
tradicts known facts of palaeontology, for the Fauna and Flora
of remote ages display a definite system of classes, orders,
families, genera and species, just as do those of the present day,
and not a chaos of imperceptibly slight variations, such as
the theory of selection requires.
For these reasons most naturalists have by this time
abandoned the theory in its exclusive form. An eminent
1 Der Darwinismus und die Naturforschung Newtons und Cuviers, I. Cf.
also G. Wolff, ' Beitrage zur Kritik der Darwinschen Lehre ' (Biolog. Zentral-
blatt, X, 1891, Nos. 15 and 16) ; 0. Hamann, Entwicklungslehre und Darwinis-
mus, Jena, 1892, chapter ix ; A. Goette, ' t)ber den heutigen Stand des Dar-
winismus ' (Die Umschau, 1898, Part 5) ; Aug. Pauly, Wahres und Falsches
an Darwins Lehre, Munich, 1902 ; Lamarckismus und Darwinismus, Munich,
1905 ; Max Kassowitz, * Die Krisis des Darwinismus ' (Die Zukunft, February
15, 1902) ; E. Dennert, Am Sterbelager des Darwinismus, Stuttgart, 1905 and
1906; H. Kranichfeld, 'Die Wahrscheinlichkeit der Erhaltung und der
Kontinuitat giinstiger Varianten in der kritschen Periode ' (Biolog. Zentral-
Uatt, 1905, No. 20 ; 1906, No. 8) ; Chr. Schroder, ' Kritische Beitrage zu den
strittigen biologischen Fragen der Gegenwart ' (Natur und Schule, V, 1906,
Part 6, pp. 233-247) ; 0. Zacharias, ' Planktonforschung und Darwinismus '
(Zoolog. Anzeiger, XXX, 1906, Nos. 11, 12, pp. 381-388).
DARWIN'S THEOEY OF SELECTION 261
modern zoologist, Dr. Hans Driesch^ condemned it perhaps
rather harshly in the BiologiscJies Zentralblatt for 1896, p. 355,
when, in speaking of Darwinism, he said : ' It is a matter of
history, like that other curiosity of our century, Hegel's
philosophy. Both are variations on the theme " how to
take in a whole generation," and neither is very likely to
give ages to come a high opinion of the latter part of our
century.' In the same publication for 1902, p. 182, he says :
' For men of clear intellect, Darwinism has long been dead,
and the last argument brought forward in support of it * is
scarcely more than a funeral oration in accordance with the
principle De mortuis nil nisi bonum, and with an underlying
conviction of the real weakness of the subject chosen for defence.'
Professor Oskar Hertwig, Director of the Anatomical and
Biological Institute at the University of Berlin, expressed
himself almost as strongly in an address delivered at the
meeting of German naturalists at Aix-la-Chapelle, on September
17, 1900, on the growth of biological knowledge in the
nineteenth century. He points out the necessity of distin-
guishing clearly between the theory of evolution and the
theory of selection, and then continues (p. 15) : * They
stand on a very different foundation and basis, for we might
say with Huxley : " The theory of evolution would stand
where it did, even if Darwin's hypothesis were blown away."
In the former we have a permanent achievement of our century,
based upon facts, and certainly worthy to be numbered among
the chief attainments of our age.' We shall have to examine
later on to what extent the theory of evolution is really based
upon facts.
In one of his lectures given in April 1905, at the Berlin
Singakademie, even Ernst Haeckel frankly acknowledged,
in at least one passage,3 that the theory of natural selection
alone ought to be termed Darwinism in the stricter sense, and
he added : ' We cannot now discuss the extent to which this
theory is justified, nor how far it has been amended by other
1 The reference is to a paper by L. Plate in the VerJiandlungen der Deutschen
Zoologischen Gesellschajt for 1899 : « Die Bedeutung und Tragweite des Darwin-
schen Selektionsprinzips.' The paper has since appeared in an enlarged form
with title : Uber die Bedeutung des Darwinschen Selektionsprinzips und
Probleme der Aribildung, Leipzig, 1903.
2 Der Kampf urn, den Entwicklungsgedanlcen, Berlin, 1905, p. 20.
262 MODERN BIOLOGY
newer theories, such as Weismann's Germ-plasm theory (1884)
and de Vries' theory of mutation.' He did not refer to this
delicate question in his later lectures. The passage is particu-
larly noteworthy, because Haeckel, as the * Prophet of Dar-
winism,' has for nearly forty years been confusing Darwinism
and the theory of evolution to suit his own ends, and has
extolled Darwin's theory of selection as the highest intellectual
achievement of the nineteenth century, because it teaches
us how to understand design in nature without recognising
a wise Creator ! And, after all, Haeckel himself finally acknow-
ledges that the confusion between Darwinism and the theory
of evolution is a mistake, and he can scarcely find any scientific
justification for the theory of selection. I feel inclined to
put on Darwin's lips the words * Et tu, Brute,' uttered by the
dying Caesar !
This confession on Haeckel's part must have been very
unwelcome to those who support Darwinism from the point of
view of popular science, and who try to mislead the general
public by confusing it with the theory of evolution. One of
them, E. H. France, in a work entitled ' Die Weiterentwicklung
des Darwinismus ' (* The further development of Darwinism '),
1904,1 has tried to represent all the progress made by the
theory of evolution since Darwin's time, and even modern
vitalism itself, as a triumphant ' further development ' of
Darwinism, whereas in reality he is uttering a sort of funeral
oration over it.
That Darwinism and the theory of evolution are two
essentially different things is quite evident from the evolution
theories of Mivart,2 Wigand,3 Kolliker,4 Heer,5 Nageli,6 Eimer,7
1 Gemeinverstdndliche Darwinistische Vortrdge und Abhandlungen, published
by W. Breitenbach, Part 12. To show the method of proof adopted by
France, I may mention that in the above-mentioned work (p. 24), by means
of unmistakable falsification of a quotation from Stimmen aus Maria-Laach,
he tries to make out that the Jesuit Father Wasmann is a supporter of the
theory of permanence, in order thus to render ' Jesuitical science ' harmless
from his point of view.
a The Genesis of Species, London, 1871.
s Die Genealogie der Urzellen als Losung des Deszendenzproblems, Brunswick,
1872.
4 ' Allgemeine Betrachtungen zur Deszendenzlehre ' (Abhandl. der Senken-
bergschen Naturforschenden Gesellsch., VIII, 1872, pp. 206-237).
5 Urwelt der Schweiz, Zurich, 1883, chapter 18.
6 Mechanisch-physiologische Abstammungslehre, Leipzig, 1884.
7 Die Entstehung der Arten, I, Jena, 1888 ; II, Leipzig, 1897,
NEO-DAftWINlSM 268
de Vries,1 Gulick 3 and others, who either attack Darwin's
principle of selection, or impose very strict limitations upon it.3
Kolliker and Eimer's theories unfortunately resemble Dar-
winism in having a mechanical and monistic basis,4 but they
have the great merit of combating it on scientific grounds, for
they admit internal causes of evolution as the chief factors
in the hypothetical phylogeny of living organisms. Eimer's
researches into evolution proceeding towards some definite
aim (orthogenesis) were continued after his death by his
pupils, Countess Maria von Linden and Dr. Fickert. It is
worth noticing that E. Strasburger, the well-known botanist,
who formerly upheld the theory of selection, has recently
given it up very decidedly.5 It is true that there are still
at the present day in Germany some eminent zoologists,
especially Professor August Weismann at Freiburg im Breisgau,
who profess to defend Darwin's theory of the all-importance
of natural selection,6 but on closer examination Weismann's
' Neo-Darwinism ' also appears to be gradually beating a
retreat, the first stage in which is marked by W. Koux's ' His-
tonal Selection,' or selection of the tissues ; Eoux tries to
supply the deficiencies of the principle of selection by trans-
ferring Darwin's personal selection to the struggle among
the various parts in the living organism. When, therefore, in
1895, Weismann propounded his theory of germinal selection,
as the last bulwark of the principle of selection, he acknowledged
that not Darwin's natural selection, but interior causes of
eVolutioii, iiilisJ^J^ t.hq nhiflf fflp-tor in a.n orderly evolution
of the organic world.7
1 Die Mutationstheorie, Versuche und Beobachtungen uber die Entstehung von
Arten im Pflanzenreich, I, Brunswick, 1901 ; II, ibid., 1903.
2 Rev. John T. Gulick, Evolution racial and habitudinal (Theory of
Divergence), Washington, Carnegie Institution, 1905.
3 In his Konvergenz der Organismen, Berlin, 1904, H. Friedmann has even
attempted to substitute the principle of divergence for that of descent. I
cannot say that I think his attempt successful ; the two principles are com-
plementary to one another, but neither can take the place of the other.
4 With regard to Kolliker's theory see an article by Professor Stolzle, ' A. von
Kollikers Stellung zur Deszendenzlehre,' Miinster i. W., 1901 (Natur und
Offenbarung, 1901). On the principles underlying Eimer's theory of ortho-
genesis see Wasmann, ' Die Entstehung der Arten nach Eimer ' (Natur und
Offenbarung, 1889, pp. 44, &c.).
5 Cf. Jahrbucher fur wissenschajtliche Botanik, 1902, pp. 518, &c.
6 Cf. Weismann's 'Lectures on the Evolution Theory,' Eng. trans.,
London, 1904.
7 See remarks in Chapter VI, p. 176.
264 MODEEN BIOLOGY
In the scientific theory of descent, selection is now regarded
as a subordinate factor of more or less importance, but it
cannot take the place of the interior factors determining
the evolution of the race, in fact it presupposes their existence.
0. Hertwig remarks very aptly on this subject (' Allgemeine
Biologie,' 1906, p. 620) : * It seems to me perfectly plain that
no advantage is gained by the use of such phrases as " Struggle
between the parts of an organism," " intraselection," " histo-
logical selection," " germinal selection," they do not enable us
better to understand the processes of organic nature. They
teach us no more about what goes on within the organism
than a chemist would learn about the formation of any organic
compound, if he were to content himself with using such a
phrase as " the struggle of the molecules in a test-tube " for
explaining some chemical process.'
Neo-Lamarckism stands in direct contrast to Weismann's
Neo-Darwinism. In 1809, Jean Lamarck wrote his ' Philosophie
Zoologique,' in which he traced the development of species to
direct functional adaptation, viz. to the principle of the
use or disuse of organs ; from this followed inevitably the
theory that the qualities thus acquired by the individual
could be transmitted to his descendants. Charles Darwin
did not by any means exclude the principle of direct adaptation
and the power of transmitting acquired qualities, but he
assigned to them less importance than to natural selection.
Weismann, however, and the Neo-Darwinists after him,
denied the possibility of direct adaptation and the trans-
mission of acquired qualities. According to them, nothing
was inherited but modifications working directly upon the
germ-plasm. This view was opposed by the Neo-Damarckians
under the guidance of Herbert Spencer and K. von Nageli,
who upheld the principle of direct adaptation, and maintained
that acquired qualities could be transmitted. Among the
modern representatives of Neo-Lamarckism we may mention
particularly two zoologists, viz. Oskar Hertwig ] and L.
Hatschek,2 E. Koken, a palaeontologist,3 and B. von Wettstein,
1 Allgemeine Biologie, Jena, 1906, esp. chapters 27-30.
2 ' Hypothese der organischen Vererbung ' : an address delivered at the
seventy-seventh meeting of German naturalists at Meran, Leipzig, 1905.
3 ' Palaontologie und Deszendenzlehre ' ( Verhandl. der 73 Versammlung
deutscher Naturforscher zu Hamburg, I, Leipzig, 1902, pp. 221, &c.).
NEO-LAMABCKISM 265
a botanist.1 As a matter of fact, both direct adaptation and
selection seem to take part in the processes of evolution ; the
former to a greater degree than the latter, because it results
from the interior laws of evolution, whilst selection only plays
the negative part of eliminating the unfit. It is self-evident
that only those modifications can be hereditary which in
some way have stamped themselves on the germ-plasm, but
how and to what extent the characteristics acquired by
individuals are transmitted to the germ-plasm, is a very dark,
mysterious question.2 Oskar Hertwig in his 'Allgemeine
Biologie,' p. 598, has made a suggestion which is certainly
very important in connexion with the theory of evolution.
He says : ' Is it not possible that, just in the same way as the
multicellular organism develops, by epigenesis from the egg,
so, when we survey the matter from the point of view of the
theory of descent, each species may develop in accord-
ance with a permanent, regular principle of progress, not
as the plaything of chance, but with the same interior neces-
sity as, in ontogeny, the blastula must grow out of the
gastrula ? '
Second. — We can give a still shorter answer to the question
regarding the extension of Darwin's theory of selection, so as
to make of it a realistic and monistic cosmogony3 — it is simply
a mischievous act committed in the name of science.
It is mischievous philosophically, because it traces back
the origin of all conformity to law in the natural order to a
denial of all conformity to law as to its primary cause. It
is mischievous theologically, although it vaunts itself to be
1 Uber direJcte Anpassung, Vienna, 1902 ; Der Neolamarckismus und seine
Beziehungen zum Darwinismus, Jena, 1903.
2 In his book * Lamarckismus und Darwinismus, Munich, 1 905, A. Pauly
aims at adducing fresh psychological evidence in support of Lamarckism.
His ideas on teleology are, however, mostly wrong and psychologically without
foundation.
3 The physical arguments in favour of this extension are stated in Haeckel's
Riddle, of the Universe, but they have been submitted to a very destructive
criticism in a work entitled Hegel, Haeckel, Kossuth and the Twelfth Com-
mandment, by 0. D. Chwolson, Professor of Physics at the University of St.
Petersburg, and author of a valuable textbook of Physics, that has been
translated" into German. We may assume that everyone knows the sharp
criticisms pronounced upon Haeckel's Riddle of the Universe by Professor
Paulsen in his Philosophia militans, by Professor Loofs in his Antihaeckel, by
Professor Seeberg and others. E. Dennert's popular works, Die Wahrheit
uber Ernst Haeckel und seine Weltrdtsel (Halle a. 8., 1904) and Haeckels Weltan-
schauung, Stuttgart, 1906, are very well worth reading.
'266
MODERN BIOLOGY
the ' Religion of the Future,' for it alters the conception of
God, the most perfect Being, and reduces it to absolutely
nothing, whilst ostensibly preserving it ; hence it would be
more honest to call it atheism than monism. Finally Haeckel's
cosmogony is mischievous socially, and constitutes one of the
greatest dangers for human society, inasmuch as it proclaims
the * struggle for existence ' and the accidental ' survival of
the fittest ' to be the only laws in the natural order, and it
exalts them to be the only laws governing human society
also. Haeckelism is, therefore, the support of anarchy and of
social democracy, as Bebel once informed^ us in the German
Parliament.1""
Third. — We saw that the third use of the name Darwinism
was to designate the application to man of Darwin's theory
of selection.3 If man is really nothing more than a higher
animal, if God does not exist for him, nor an immortal soul,
nor any retribution beyond the grave, then human society
is indeed delivered over to anarchy, and the anarchists are the
only sensible people. But to uphold such a doctrine in the
name of science is worse than humbug, it is a grievous offence
against the highest possessions of mankind.3 Those periodicals
are guilty of participation in this offence, which profess to
present science in a popular form, and recklessly represent
the application of Darwinism to man as justified by assured
scientific results. Even men like Rudolf Virchow, who do not
1 In his well-known speech on September 16, 1876, in which he proved the
connexion between social democracy and Darwinism, that Haeckel denied,
Bebel's words were : ' Gentlemen, in my opinion Professor Haeckel, the
decided advocate of the Darwinian theory, because he does not understand
social science, has no idea at all that Darwinism must necessarily promote
socialism, and vice versa, socialism must harmonise with Darwinism, if its
aims are to be correct.' Cf. also a little pamphlet, Darwinismus und Sozial-
demokratie, oder Haeckel und der Umsturz, Berlin, 1895. It is a matter of
especial psychological interest that recently even anarchists have attacked
the theory of the struggle for existence. The Russian anarchist, Prince Peter
Kropotkin, has done this in his book on mutual help in development, which
G. Landauer translated into German, Gegenseitige Hilfe in der Entwicldung,
Leipzig, 1904. Even to men of this type the theory of selection is beginning
to seem untenable, but apparently they do not see that, by acknowledging
this fact, they are undermining the foundations of their own social theories.
2 A further discussion of this subject will be found in Chapter XI.
3 For a scientific criticism of Darwin's theory of the descent of man, see
the works of Hamann and Ranke, mentioned on p. 258 ; also J. Bumiiller,
Mensch oder Affe ? Ravensburg, 1900 ; C. Gutberlet, Der Mensch, sein Ursprung
und seine Entwicklung, Paderborn, 1903 ; Wilh. Schneider, Gottliche Weltordnung
und religionslose Sittlichkeit, Paderborn, 1906.
THE SCIENTIFIC THEOKY OF DESCENT 267
claim to speak from the point of view of Christianity, have
felt bound to protest vehemently against this mischievous
doctrine.
3. THE SUBJECT OF THE DOCTRINE OF EVOLUTION AS A
SCIENTIFIC THEORY
It is high time for us to go on to the real question under
discussion, and ask : ' What are we to think of the theory
of evolution in itself ? Have the systematic species always
existed in their present forms, or are they mostly related with
other species, some still existing, and others extinct, and
known to us only by fossil remains dating from earlier ages
of the world ? Are they the result of an historical evolution
of the organic world, or were they originally created in their
present condition ? '
In order to be able to deal with this important question
objectively and impartially, it is indispensable for us to
disregard altogether the misuse made of the theory of evolution
by those who distort it to answer the purposes of atheistic
materialism. It is much to be regretted that this misuse of it
occurs. It is embodied in Haeckelism, which is by no means
a feather in the cap of modern science. Nothing has more
injured the reputation of the theory of descent — as the doctrine
ot evolution is called in scientific circles — than the fact that
one_ section of atheists and materialists have used it as a
battering-ram against Christianity ; nothing has done more to
vulgarise it and disfigure its" scientific character than this
misuse of it, which has rendered it almost unrecognisable.
It is chiefly owing to this misuse, that those who profess to
be Christians regard the theory of descent with so much
suspicion, and think themselves bound to hold aloof from it,
because they confuse the anti- Christian character thus given
it with the essence of the theory of evolution. We must
resolutely put aside all thoughts of this misapplication, and
consider the doctrine of evolution as what it really is, viz,
a scientific theory, which we may either accept or reject Ton
its own merits.,
nrepeat7"we have to consider the doctrine of evolution
as a scientific theory, which arises out of the facts of the
268 MODEBN BIOLOGY
organic world, and seeks to offer the best and simplest natural
explanation of them, in accordance with strictly logical methods
of thought. We are not concerned with that pseudo-theory of
descent,1 which, starting from the a priori, considerations of a
false philosophy, takes as its fundamental axiom : ' We
refuse to admit the existence of a personal Creator, and there-
fore, whatever exists, must have developed itself by purely
mechanical means.' No less false than this fundamental
principle are, of course, the various so-called postulates, which
the pseudo-theory of descent is fond of stating in the name
of science. In the name of true science we are forced to oppose
an emphatic veto to these postulates, for the methods of this
theory of descent are utterly antagonistic to those of true
scientific procedure. We must take up, however, another
attitude with regard to the question what we are to think
of the theory of evolution, from the point of view of natural
science. We need not feel any scruple about attempting
to answer this question, for we lay down no false postulates
of materialism, but we approach it taking as our starting
points real facts, viz. the works of God in nature.
Why should we fear to look the truth in the face ? We
know with absolute certainty that one truth can never contra-
dict another, therefore the recognition of what is really true
in the theory of evolution can tend only to the glory of Him
who is the highest and eternal Truth.3 Let us, therefore, try
to give an honest and careful answer to the question : ' What
is the scientific value of the modern theory of evolution ?
What does it explain ? How far is it necessary to a scientific
comprehension of the organic world about us ? '
Is the theory of descent able to account for the origin
of organic creatures and of organic life on our earth ? No,
1 The advocates of Haeckelism are doing their best to identify this pseudo-
theory of descent with the scientific theory of evolution. An instance of this
was given by H. E. Ziegler, in an address delivered at the seventy-third
meeting of German naturalists at Hamburg on September 26, 1901, and
printed at Jena, 1902, with the title : fjber den derzeitigen Stand der Deszen-
denzlehre in der Zoologie. ^ It is the counterpart of Haeckel's address delivered
in Cambridge in 1898 : Vber unsere gegenwdrtige Kenntnis vom Ursprunge des
Menschen, Bonn, 1899. Haeckel's influence on Ziegler is plainly apparent in
the latter's Hamburg lecture (cf. for instance pp. 18, 19, 24, 28, 43, &c.).
I think it unnecessary for this reason to criticise Ziegler's views mere fully.
2 On this subject see J. Knabenbauer, S. J., ' Glaube und Deszendenztheorie '
(Stimmen aus Maria-Laach, XIII, 1877, pp. 71, &c.).
THE SCIENTIFIC THEOKY OF DESCENT 269
it cannot, for it is a theory of natural science, and natural
science can tell us nothing of the source of life on our planet.
It only knows the facts and the laws to be deduced -from them.
But, however carefully we compare these laws with one
another, and however skilfully we combine them, they give
us no suggestion of spontaneous generation, i.e. of the spon-
taneous development of living creatures from lifeless matter ;
on the contrary, modern biology is directly opposed to the
theory of spontaneous generation (cf . Chapter VII, ' The Cell
and Spontaneous Generation '). If, therefore, a modern
scientist, acting not as an investigator of nature, but as a
monistic * philosopher,' appeals to natural science for evidence
that the assumption of spontaneous generation is * a postulate
of science,' he is entangling himself in a very obvious contra-
diction. What biology actually knows is nothing but an
uninterrupted series of living beings, living cells, living
nuclei, which find a truthful expression in the fourfold law :
omne vivum ex vivo ; omnis cellula ex cellula ; omnis nucleus
ex nucleo ; omne chromosoma e chromosomate. The student of
nature must necessarily accept these laws as a foundation,
if he wishes to trace the origin of life on earth, but they will
carry him no further — they will lead him round in a circle
and never let him see the beginning of the mystery. If, as
a philosopher, he wishes to study the origin of life more deeply,
he is forced to conclude that only some cause apart from the
world could have produced the first living organism out of
matter. We have already discussed this point in the section
dealing with spontaneous generation (pp. 204, &c.). If the
student of nature refuses to accept this conclusion, and is
resolved to be content with what natural science as such can
offer him, he must simply say : * We know nothing about the
origin of life.' Many naturalists of the present day have
actually adopted this empirical standpoint ; it was done,
for instance, by Branco in the address that he delivered on
the occasion of his admission to the Eoyal Academy of Science
in Berlin (' Sitzungsberichte der Koniglichen Akademie der
Wissenschaften,' 1900, pp. 679-696).
What, then, are we to think of the theory of evolution ? It
certainly does not profess to account for the origin of organic
life on earth, it has simply to accept it as a fact ; and at the
270 MODEEN BIOLOGY
same time it accepts as a fact the existence of laws governing
organic development. Just as philosophical examination
has as its necessary foundation the fundamental principles
of thought ; just as no human being can think over any
philosophical problem without assuming that his understanding
is able to recognise the truth, that everything must have a
sufficient cause, and that two contradictory propositions cannot
both be true at the same time ; so no student of nature can
consider theories of evolution, unless he assumes at the outset
as a fact the existence of laws governing organic evolution.
If he refuses to admit that essentially the same laws of organic
formation, which now govern the genesis of living creatures,
were in force from the very beginning, he has no clue at all to
his phylogenetic research ; as soon as he tries to set aside
this fundamental principle, his scientific investigations become
mere fictions, with no basis of fact. Therefore, in considering
the race-evolution of living organisms, we must never lose
sight of the conclusions stated at the end of Chapters VI and
VIII (pp. 176, &c., and pp. 247, &c.). In dealing with the
race-evolution of the living things about us, we can far less
dispense with internal laws of evolution, which are the ex-
pression not of a purely mechanical, but of a higher, vital
activity, than we can dispense with them in dealing with the
phenomena of fertilisation, heredity, and ontogeny.
What is, then, the real scope of the doctrine of descent, in
so far as it has a scientific basis ? Its task is, and can only
be, to determine the sequence in which the organic forms
appeared upon earth, and so to establish their relationship
with one another ; it has, moreover, to investigate the causes
underlying the gradual modifications in organic forms. The
task of the theory of descent is, in other words, to examine
the actual facts and causes of the sequence of organic forms,
chief amongst which are the species of the present time, being
the last offshoots of one or many hypothetical pedigrees.
The theory of evolution is not, and cannot be, an empirical
science (cf. p. 253 in § 1), because it is concerned with the
earliest history, antecedent to that of the present organic
world, By collecting traces of that evolution from the fossil
records of palaeontology and by comparing them with the
facts of the present, it becomes a theory in natural science,
SCOPE OF THE THEOKY OF DESCENT 271
aiming at offering a probable explanation of the connexion
between these actual phenomena.
From what has been said of the limitations of the theory
of descent, it follows that it is by no means essential for it to
trace the origin of all living organisms back to one single primi-
tive cell. Nor need it be thus restricted within the limits of
the animal and vegetable kingdoms respectively, and trace all
animals back to one stock, and all vegetables back to another.
It is not essential to the theory of evolution to insist upon a
monophyletic evolution ; it may just as well decide in favour
of a polyphyletic evolution, for, in examining the hypothetical
race-evolution of living organisms, it is bound to conform to
facts, and not to monistic postulates. As I shall show later,
facts point to a polyphyletic evolution among both animals
and plants. Whether a monophyletic or a polyphyletic evo-
lution is to be accepted is therefore, for the scientific theory
of descent, a question of fact and not of principle.
From this we may deduce two statements that are important
in our investigation : 1st. The extreme champions of the
theory of descent, who recognise only a monophyletic evolution
as the real theory of descent, and reject polyphyletic evolution
as being merely the theory of permanence in disguise, are
influenced by monistic prejudices and not by a genuinely
scientific spirit ; l they completely misunderstand what the
scientific doctrine of evolution really is. 2nd. Equally mis-
taken is the attitude of those opponents of the theory of
descent, who try to prove that the whole doctrine of evolution
has broken down, because no one has yet succeeded, and prob-
ably no one ever will succeed, in tracing back the chief types
of the animal and vegetable kingdoms to one single stock.
I cannot therefore concur with Fleischmann's opinions, ex-
pressed in his book ' Die Deszendenztheorie ' (Leipzig, 1901).
In many passages he bases his arguments against the theory
of descent on the statement that the types of organisation among
animals cannot phylogenetically be derived from one single
type. This proves nothing but that polyphyletic evolution
must be accepted rather than monophyletic ; it does not
1 1 wish this remark to be taken to heart by Escherich, Forel, Haeckel, von
Wagner and others, who criticised my first edition. See also ' A Few Words
to my Critics,' at the beginning of this volume.
272 MODEEN BIOLOGY
prove that an evolution of the species within definite series
of forms or genera is impossible. Arguments of this kind
affect only the monistic, and not the scientific, theory of
descent. In general, I am unable to share Fleischmann's
views, which are involved in pure empiricism and agnosticism.
4. THE THEOEY OF EVOLUTION CONSIDERED IN THE LIGHT
OF THE COPERNICAN THEORY OF THE UNIVERSE
' But/ some one may say, ' why do we not simply assume
that the species in the world of organic life have always been
what they are at the present day ? Why do we want any
theory of evolution at all ? '
I am bound to explain this point to my readers, at least
to some extent, before I go on to discuss the modern theory of
descent more in detail. Three hundred and fifty years ago,
when war broke out between the old Ptolemaic view of the
universe and the new Copernican view, people had no con-
ception of the distance to which they would be carried by the
ideas that then took possession of the human intellect. It was
not until the nineteenth century, that from the heliocentric
theory of the universe inferences were made affecting the
natural development of our solar system, and the whole history
of the universe, of which the geological development of our
earth occupies but an insignificant moment of time. And
within this insignificant period (which, in comparison with the
development of the whole universe, is like a second between
two eternities, although according to geologists it really lasted
millions of years) is another period of history preceding that
in which man appeared upon the world, and this is the history
of the animal and vegetable kingdoms from the earliest
palaeozoic age until the present time.
The Copernican system revealed to us the earth as a mere
atom in the universe, as one of the many planets attendant
upon a central sphere, that we call the sun. But our sun is
not the only sun ; there are thousands of others, many being
still far larger than it is. All the innumerable fixed stars that
we see in the sky at night are so many suns, which are not,
however, scattered at random in space, but form one single
huge cosmic system. This system is not an unalterable
THEORIES REGARDING COSMOGONY 273
mathematical formula in its various components. Astronomy
teaches us that the constellations are, at different stages in
their evolution, ranging from gaseous vapour to molten matter
like the sun, and even to the dark planets, that are visible
only by the light of others.
This is where the theories of Kant and Laplace on cos-
mogony find their points d'appui ; they strive to account for
the genesis of the whole universe by one uniform law.1 By
means of the laws which now control the movements and
conditions of the celestial bodies, this cosmogony seeks to
ascertain how our solar system, and the cosmic system as a
whole, assumed their present form. It was led to accept
the existence of an original enormous sphere of gas, in which,
as it gradually cooled and condensed, a rotatory movement
arose, that caused the formation of the solar systems. Accord-
ing to the same cosmic laws, the planets subsequently separated
from each sun, in order to circle round it on definite paths.
And one of these planets is our earth. Many modifications
have recently been introduced into the theories that are called
after Kant and Laplace,3 but it is not likely that any new
theory will take its place, at least as far as its essential
outlines go.
T. C. Chamberlin's ' Spiral Nebulae Theory ' 3 suggests
a different explanation for the origin of the planetary system
of a sun, but still it presupposes the existence of the gaseous
sphere.
No matter what scientific form the theories regarding
cosmogony may take, their problem is always to account for
the present form and arrangement of the heavenly bodies,
and to explain how this form and arrangement may have
been evolved by natural means.
At the present day there are probably very few who still
cling to the old theory that sun, moon, earth, planets and
1 Cf. J. Epping, S.J., Der Kreislauf im Kosmos, Freiburg, 1882 (Supplement
to Stimmen aus Maria-Laach, Part 18} ; also an excellent work by K. Braun, S. J.,
Uber Kosmogonie vom Standpunkt christlicher Wissenschaft, Miinster, 1905.
2 The theories of Kant and Laplace on cosmogony are somewhat different,
and cannot be united under one name, as Stolzle, Gockel, and other recent
authors have shown. See A. Gockel, Schopfungsgeschichtliche Theorien.
Cologne, 1907.
3 Cf. F. R. Moultpn, 'The Evolution of the Solar System' (Astrophysical
Journal, XXII, 1905, pp. 165-181). See also the review in the Naturwissen-
schajtliche, Rundschau, 1906, No 5, pp. 53-56.
274 MODEKN BIOLOGY
all the fixed stars in the universe were created once for all as
we now know them. Even to St. Augustine it seemed a more
exalted conception, and one more in keeping with the omni-
potence and wisdom of an infinite Creator, to believe that
God created matter by one act of creation, and then allowed
the whole universe to develop automatically by means of
the laws which He imposed upon the nature of matter.
God does not interfere directly with the natural order
when He can work by natural causes : this is a fundamental
principle in the Christian account of nature, and was enunciated
by the great theologian Suarez,1 whilst St. Thojnas_Aq[uinas
plainly suggested it long before, when he~regarded it as testi-
mony to the greatness of God's power, that His providence
accomplishes its aims in nature not directly, but by means
of created causes.2
Is it not reasonable for us to try to apply the same principle
of independent evolution also to the living creatures that
inhabit our globe ? The obvious complement to the geological
history of our world is the history of the creatures that have
dwelt on it, since the time when organic life first made its
appearance. In the geological arrangement of strata we see
the working of natural forces influencing the formation of
the earth's surface, and, in the same way, in the fossil animals
and plants we see the remains of organisms that really lived
at those respective epochs.3
Palaeontology teaches us that our present species of
animals and plants have not always existed. It shows us
that there was a succession of different organic forms in the
1 De opere sex dierum, 1. 2, c. 10, n. 12. Further evidence to show that this
idea was by no means strange to St. Augustine, St. Thomas, St. Bonaventure
and others may be found in Father Knabenbauer's ' Glaube und Deszendenz-
theorie ' (Stimmen aus Maria-Laach, XIII, 1877, pp. 75, &c.). Cf. also T. Pesch,
Philosophianaturalis, II, pp. 241, &c., and Die grossen Weltrdtsel, II, pp. 349, &c.
2 Summa c. gent., 1. 3, c. 77.
3 The idea that fossils were originally created as such, and represent mere
lusus naturae, is just as groundless as the other opinion, that all fossils date
from the deluge. The first idea is wrong in principle, and contradicts the
fundamental laws of all intelligent research ; it is opposed, therefore, to the
true philosophy of nature, and leads inevitably to occasionalism, and is equi-
valent to a complete abandonment of all hope of giving a natural account of
palseontological facts. The second theory may not be intended to clash with
geology and palaeontology, but it is manifestly wrong in assuming that all the
strata containing fossils, more than 20,000 in number, can be accounted for
by the deluge.
EVOLUTION OR CREATION? 275
various geological periods, and in this succession the species
of animals and plants that appeared later approximated more
and more closely to those of the present time, and in many
cases — e.g. in the extinct connexions of the horse — the
succession suggests upward lines of evolution,1 and our present
species are their latest developments.2
We have now to face the critical question : ' Does this
gradual or more abrupt approximation of the fossil Fauna
and Flora to those of the present depend upon a mere succession
of forms, constantly becoming more like the present forms,
or is it a real evolution, a genetic production of various
systematic species from one another ? Are these " evolutionary
series," which lead us from fossil ancestors to now existent
species, merely apparent ? Do they owe their origin to the
fact that, at the close of the various geological formations
and groups of formations, a great catastrophe occurred, destroy-
ing all living creatures, which at the beginning of the next
period were replaced, by means of a new creation, by similar
creatures, for the most part somewhat more highly organised ?
Or are these evolutionary series real and natural, depending
upon a genealogical connexion between the organisms of
various periods ? '
There can scarcely be any doubt as to the answer. Cuvier's
theory of a catastrophe has been given up by geologists, because,
when generalised, it proved to be inconsistent with facts ;
consequently it had to be given up by palaeontologists also,
In place, therefore, of the periodically repeated ' new creations/
the theory of a natural evolution of organic forms has won
1 The hypothetical pedigree of the Equidae does not, however, form a simple
line of evolution, but it has many ramifications, and since the Lower Eocene
age they have developed on distinct lines in Europe and North America. Cf.
Zittel, Grundziige der Paldontologie (Munich and Leipzig, 1895), p. 871.
2 I am not, however, speaking here of evolutionary series in the sense of
Darwin's theory of transmutation, i.e. not of series of very small and gradual
transitions, for these, if they occur at all, are an exception to the more usual
transitions * by steps,' that involve greater changes. Hilgendorf's famous
Planorbis series has proved not to be a progressive sequence of variations,
but rather a cycle of recurring variations, and it is of no use for the purposes
of phylogeny. (Cf. K. Miller, ' Die Schneckenfauna des Steinheimer Obermio-
cans,' in the Jahreshefte fur vaterldndische Naturkunde in Wurttemberg, 1900,
pp. 385-406 with Plate VII.) L. Doderlein's dictum (Zeitschrift fur Morphologie
und Anthropologie, IV, 1902, Part 2, p. 408) that complete knowledge of any
group of animals requires all the forms in that group to stand in unbroken
sequence, is not based on fact, but is a theoretical postulate of the Darwinian
theory of evolution.
T2
276 MODERN BIOLOGY
acceptance,1 in logical application of the principle that God
does not interfere directly with the natural order, when He
can work by natural causes.
The theory of evolution, regarded without prejudice,
is then for us the latest outcome of the Copernican theory of
the universe, which no one probably, at the present day, will
call un-Christian.
A few instances may be added by way of illustration.
If we find the Brachiopod Order Lingula occurring frequently
in the Silurian and Devonian strata, and continuing to appear
at different geological epochs in various species down to the
present day, we must undoubtedly say : ' The modern species
of Lingula are really connected with those of the Silurian age ;
in fact they are their modified descendants.' If in the
Cambrian, the oldest strata containing any fossils, we find
representatives of the family of Nautiloidea, various genera
and species of which still exist, we must say in the same way :
* The still existing four species of Nautilus are modified descen-
dants of members of the same family belonging to earlier
ages of the world.' If we compare our crickets (Phasmidae)
with those of the Carboniferous period, we shall be forced
to ascribe to them not merely a theoretical, but a real relation-
ship with the Protophasma and the Titanophasma of the coal
age. If we compare our ants and Paussidae with those found
in Baltic amber of the Tertiary period, we cannot possibly think
that they are new creations, but must regard them as genuine
descendants of the Tertiary forms, although differing from
them partly specifically and partly generically. Any other
view of the matter seems scientifically almost impossible.
If we compare fossil termites 2 with those of the present
1 It is a remarkable fact that more than two hundred years ago, a famous
Jesuit, Father Athanasius Kircher, in his book, Area Noe in tres libros digesta
(Amsterdam, 1675), expressed his belief that our modern species had originated
by transmutation within definite series of forms. (On this subject see Daniele
Rosa, « II Rev. Padre Kircher trasformista,' Bolletino dei Musei di Zoologia
ed Anatomia comparata d. R. Universith di Torina, XVI, No. 421, March 14,
1902.) Although Father Kircher's views were based on insufficient data, we
are all the more justified in holding similar opinions, as our scientific knowledge
is much greater.
2 According to Handlirsch, remains of termites occur with certainty
only after the early Tertiary period ; he does not regard as termites what
Heer described as such occurring in the Black Jurassic strata. His views,
however, do not in any way affect the above statement respecting the connexion
between our present termites and those of the Tertiary period.
EVOLUTION OE CKEATION ? 277
day, we cannot doubt that they all form one single natural
stock, continuing from the Mesozoic group of formations
through the Ccenozoic to the Alluvial present. The extinct
fossil genus Clathrotermes, of the black Lias, represents one
natural stock with the fossil varieties of the genus Calotermes,
belonging to the same period. Of this latter genus many
species still exist, which differ, however, from those occurring
in the lias. With regard to the much greater variety of fossil
termites of the Tertiary period, which include a great many
still existent genera and one that is extinct (Parotermes),
we cannot question the fact that they are genetically connected
both with the termites of the Lias and with those of the present
day, although their species are different both from the Mesozoic
and the modern. We still find in Australia a curious genus of
termites, Mastotermes, whose wing- veins, in my opinion, show
that they are unmistakably connected with the Palaeozoic
Blattinae of the coal age ; and this fact justifies our assuming
that we have in Mastotermes the last living representative of
the oldest and most original form of termite, which as a
' collective type ' l has united in itself the venous systems of
cockroaches and termites, that afterwards became entirely
distinct. Australia is particularly rich in old forms, which
occur in other parts of the world only in a few still surviving
representatives, or as fossils dating from earlier ages.2 These
instances are quite enough to prove that it is hardly possible
to deny the existence of a genuine race-connexion between
our modern forms of animals and the extinct species of bygone
ages. We may now return to our consideration of the doctrine
of evolution.
Under Haeckel's guidance, the monists have misused the
1 Forms which show the characteristics of several systematic groups are
called ' collective types.' Such, for instance, is Peripatus among the
Arthropods, which by its low organisation approaches the Annelids. According
to Handlirsch (VerhandL d. Zool. Bot. Gesellsch., Vienna, 1906, Part 3, p. 91),
it ought to be classed among the Annelids. Numerous collective types occur,
especially among the palaeozoic insects, to which Skudder gives the general
name of Palaeodictyoptera.
2 In support of this statement I may refer to the Monotremata and Mar-
supials among mammals, and to the genus Arthropterus in the family of
Paussidae. Australia seems to have preserved the oldest type of the human
race, for Macnamara has recently shown that the cranial formation of modern
Australian and Tasmanian blacks approximates very closely to that of the
fossil Neandertal man. We shall come back to Macnamara's statements in
Chapter XI.
278 MODEEN BIOLOGY
theory of evolution, and by making it serve as a weapon with
which to attack the theism that they hate, they have brought
it into disrepute in conservative circles ; and so the idea has
arisen that the theory of evolution is an absolutely atheistical
device, directly opposed to Christianity. I have just shown
this idea to be erroneous, and to have no foundation. If we
wish successfully to combat the modern theory of descent,
in so far as it has proved serviceable to atheism, we must
carefully distinguish truth and falsehood in it. We shall
then have no difficulty in depriving our antagonists of their
weapons, and even in smiting them with the same sword with
which they fancied we were already conquered. If we let
ourselves be misled by the skilful tactics of our monistic
opponents, and take up an attitude hostile to evolution in
every form, we shall be playing into their hands and giving
them an easy victory. We shall in fact be assuming the
same mistaken position as the champions of the Ptolemaic
system once assumed against the advocates of the Copernican
theory. They were obliged to be always on the defensive, and
to limit themselves to weakening this or that actual piece of
evidence adduced by their opponents, as not holding good.
In an intellectual conflict such a position must, in course of
time, be abandoned. A succession of retreats brings the
defenders on to more and more dangerous ground, and finally
leads to a decisive defeat. If Christianity is not to succumb
to the attacks of monism based on natural philosophy, it must
determine upon bold action on the offensive ; it must
seize the enemies' arsenal, and by accepting without reserve
whatever is right in the theory of evolution, it will turn its
opponents' weapons against themselves. In such proceedings
caution is always advisable. Not everything alleged by the
supporters of the theory of descent to be * based on actual
facts ' really deserves belief. I need only remind my readers
of Haeckel's famous pedigree of man, of which one critic
sarcastically remarked that it was just as worthy of credence
as those of the Homeric heroes. We must examine carefully
how far we can accept the ideas involved in the theory of
evolution, both from the philosophical and the scientific
points of view. There must be no mention of concessions.
We make concessions to error only when, through cowardice
PHILOSOPHY AND EVOLUTION 279
or weakness, we accept what is wrong as right, or what is half
true as quite true ; but it is not a concession when we deprive
error of the weapons that it is using in the struggle against truth.
5. PHILOSOPHICAL AND SCIENTIFIC LIMITATIONS OF THE
THEOKY OF EVOLUTION
1. What are we, therefore, to think of the theory of descent
in its relation to philosophy ? It has already been shown
that the acceptation of an evolution of the organic species is
only a logical consequence of the cosmic and geological evolu-
tion. On the philosophical side it would be possible to reject
the theory of descent only if it could be proved, on purely
philosophical grounds, that our present species are absolutely
unchangeable, and that therefore there can be no question
of their having evolved from older forms. But philosophy
cannot adduce any proof of this kind, because the subject
does not fall within her scope. She is obliged to leave natural
science to decide whether the systematic species are altogether
constant magnitudes or not, and we have already seen what
this decision is, and shall refer to it again later.
The fundamental principle laid down by philosophy with
reference to the theory of evolution agrees perfectly with
Christianity, and may be stated thus : ' It is not permissible
to assume any immediate interference on the part of the
Creator, where the facts can be explained by natural evolution.'
In applying this principle we must be careful to distinguish the
philosophical and the scientific standpoints. Many things
are possible in themselves, and even probable, a priori, but
there is no scientific proof of their occurrence. The limits
assigned to us by philosophy, with regard to our acceptance
of the theory of evolution, are far wider than those imposed
upon us by natural research as to details. Moreover, the
former are fixed and cannot be overthrown ; the latter are
constantly changing as our positive knowledge advances.
We must, therefore, carefully distinguish between the limits
set by philosophy and natural science respectively to the
theory of evolution ; and, in dealing with the philosophical
limits, we must again distinguish between purely philosophical
questions and those that are of a mixed character.
280 MODEKN BIOLOGY
Let us first consider the philosophical limits. In one
sense philosophy has only to sketch the hroad outlines of the
theory of evolution ; it is the task of natural science to fill
in the details. The first and foremost boundary, admitting
of no modification whatever, is the principle that the hypo-
thetical race-evolution of the organic species must have had
an adequate first cause. This principle contains two postulates,
one purely philosophical, and one partly philosophical and
partly belonging to natural science. The first is : ' We must
assume the existence of a personal, all-wise and all-powerful
Creator as the first cause, extraneous to the world, of the
whole cosmos and its laws of evolution/ The second is : * In
order to account for the origin of the first organisms, we must
accept some special action, direct or indirect, on the part of
the Creator upon matter.' Here we are not concerned with
1 Creation,' strictly speaking, as we are in the first postulate,
but only with the production of the primitive organisms
from already existent inorganic matter, which had been formed
by a definite act of creation at the beginning of the cosmic
evolution.1 The formation of the first living creatures followed,
therefore, by an eductio formarum e potentia materiae, as scholastic
philosophy expressed it. As intelligent beings we cannot
dispense with this postulate ; all the efforts of monism to set it
aside are fruitless. This postulate is of a mixed character,
not purely philosophical like that regarding the creation of
primitive matter, for natural science proves that an essential
difference exists between animate and inanimate substances,
and shows us the absolute incompatibility of the laws of biology
and the theory of spontaneous generation. (Cf. Chapter VII,
pp. 198, &c.) Neither philosophy nor natural science can tell
us how the first organisms came into being ; no facts that
we can observe enable us to infer anything on this subject.
Nor can philosophy say how many primitive organisms were
produced, and whether they differed essentially from one
another or not. Yet a somewhat important limitation seems
to meet us here. As sensitive life is on a higher level than
vegetative, it is reasonable to suppose that the former could
1 I wish to draw particular attention to this passage, as some of the critics
of my previous edition fell into the error of regarding the creation of the
first organisms as a creatio e nihilo.
PHILOSOPHY AND EVOLUTION 281
not have evolved itself out of the latter. We must therefore
assume that when organic forms first came into being, there
was in all probability a differentiation among them into
animals and vegetables. This postulate is of a mixed character,
partly philosophical and partly scientific, and is by no means
absolutely fixed. For, on the one hand, while observed facts
show us the great difference between the vegetative and
sensitive life of the higher animals and the merely vegetative
life of the higher plants ; on the other hand, they reveal
to us a number of unicellular organisms, which zoologists
reckon among the lower animals, and botanists among the
lower plants ; l and in their case it is impossible to say whether
the sensitiveness of the protoplasm, which is a general character-
istic of all living cells> amounts to real sensation or not.2 We
have also to take into consideration the movements made by
certain plants in response to external stimulus, for which a
purely vegetative interpretation seems inadequate,3 although
I agree with J. Keinke 4 in thinking that the so-called ' sense
organs ' of plants represent merely the receptive centres for
physical and chemical stimuli, and we are not justified in arguing
from them that plants have sense perception. We probably
ought not to regard the original difference of animal and
vegetable organisms as an unalterable philosophical postulate ;
1 On this subject see von Wettstein, Handbuch der systematischen Botanik,
I, 1901, pp. 16, &c.
2 We derive our ideas of plants and animals from the higher varieties
of both, which it is perfectly easy to distinguish, but there are obviously great
difficulties in applying these ideas to unicellular organisms.
3 Cf. Haberlandt, Die Sinnesorgane im Pflanzenreich zur Perzeption mechani-
scher Reize, Leipzig, 1900 ; ' Die Sinnesorgane der Pflanzen ' (paper read at
the seventy-sixth meeting of German naturalists at Breslau, September 23,
1904, published in the Naturwissenschaftliche Rundschau, 1904, Nos. 45 and
46) ; ' tiber den Begriff " Sinnesorgan" in der Tier- und Pflanzenphysiologie '
(Biologisches Zentralblatt, 1905, No. 13, pp. 446-451 ) ; ' Die Lichtsinnesorgane
der Laubblatter ' (ibid., No. 17, pp. 580-588). See also Fr. Noll, Das Sinnesleben
der Pflanzen, Frankfurt a. M., 1896 ; F. R. Schrammen, ' Kritische Analyse von
G. Th. Fechners Werk : Nanna oder iiber das Seelenleben der Pflanzen '
(Verhandl. des Naturhist. Vereins, Bonn, LV, 1903, pp. 133-199). On p. 198
Schrammen seems to think that we ought to ascribe to plants a sensitive,
but not an intelligent existence. This is intelligible only if he means by a
sensitive existence merely susceptibility to mechanical and other stimuli,
not amounting to perception. Many botanists speak of plants as sensitive
to light, but the word is then used inaccurately, as it is when photographic
paper is so described. It is not possible in either case to use the word ' sensitive '
in its strict psychological meaning ; we ought rather to say susceptible to
light.
4 Philosophie der Botanik, 1905, pp. 83-87 and 113.
282 MODEKN BIOLOGY
that the whole organic world may have been evolved from one
single primitive cell is not an absolute impossibility, though
it is improbable. This improbability appears greater when we
take into account the important physiological distinction
between the two kingdoms, which 0. Hertwig ('Allgemeine
Biologie/ 1906, p. 602) states as follows : * In consequence
of their characteristic metabolism, the whole formation of
chlorophyll-bearing plants is directed towards the exterior
and is visible from the exterior, but, unlike animal organisms,
plants either show no interior differentiation into organs
and tissues, or they show it in a relatively limited degree.'
Philosophy can give us no information at all regarding
the number of forms of plants and animals originally produced,
nor can it tell us whether they were produced once for all and
in one place, or on many occasions and in various places.
Natural science, too, in the present state of our knowledge,
can throw very scanty light upon this subject, but I shall
return to this topic later ; let us now consider it only from
the point of view of philosophy.
Philosophy is not concerned to decide whether the animal
world on the one hand, and the vegetable world on the other
hand, were each descended from one primitive form (mono-
phyletic evolution), or whether they originated simultaneously
or successively from several primitive forms, independent of
one another (polyphyletic evolution). Nor does philosophy
tell us anything of the causes that motive race-evolution ;
however, the fact that, as natural science shows us, at the
present time interior laws of development are the ultimate
foundation of all organic genesis,1 justifies philosophy in
inferring that the race-evolution of living organisms chiefly
and essentially must have been the result of interior causes
of development. All the exterior causes are simply aimless,
unless we presuppose the existence on the part of the organism
of a corresponding interior capacity for development ; and
this capacity must ultimately have been implanted by the
Creator in the nature of the primitive types. Therefore
philosophy is justified in drawing the further inference that
1 Some suggestions respecting the probable material bearers of these laws
of development were made in Chapter VI, pp. 164, &c. Cf. also the conclusion
of Chapter VIII.
PHILOSOPHY AND EVOLUTION 283
those theories of descent, which attach the utmost importance
to the exterior causes of development, whilst underrating
the interior, must be regarded as unsatisfactory. Thus far
philosophy may and must utter her decisions ; but in herself
she can tell us nothing as to the character of these interior
causes of development and how they co-operate with the
exterior factors ; any knowledge that she possesses on these
points is borrowed from natural science.
She does not inform us whether a race-evolution of the
organic species ever really took place or not ; she does not
tell us anything as to the number of the original primitive forms ;
she teaches us nothing about the laws governing the hypotheti-
cal race-evolution of organisms, nor the order in which it took
place. If she is wise, she will leave it to natural science to
express an opinion on these points ; l but there is one thing
of great importance, which she is able to tell us. Without
a first cause outside the world, the existence of matter and
the laws governing its development would have been im-
possible ; without the same first cause outside the world,
the origin of living organisms from inorganic matter would
have been inconceivable, and consequently a race-evolution
of the organic world would have been out of the question;
and, in exactly the same way, we can account for the existence
of man only by assuming some special action on the part of
the Creator, this special action being the creation of the human
1 The writer of a review on the first edition (in the Innsbrucker Zeitschr. fur
katholische Theologie, 1905, p. 561), asks : ' Is there philosophically no diffi-
culty in assuming that the sparrow and the hippopotamus have branched
off from the same primitive form ? Are we not forced to believe that there
is an essential difference in their inner nature, in their very soul ? ' I do not
think that this question admits of a purely philosophical answer. If it were
worded scientifically, it would be simply : ' Are birds and mammals to be
regarded as related ? ' On examining the scientific limitations of the evolution
theory we shall find that there is very little to be said in support of the common
descent of all vertebrates. Moreover, as mammals appear in the Triassic, and
birds only in the Jurassic strata, there are no intermediate forms between
birds and mammals. It is true that in some respects our present Monotremata
(Ornithorhynchus and Australian ant-eating Echidna) occupy a position
midway between these two classes of vertebrates, but in other respects there
are important differences. (Cf. Fleischmann, Deszendenziheorie, 1901, chapter i.)
If birds and mammals are two branches of a common stock, which is very
doubtful, they are still not directly related, but are only connected through
long extinct Saurians. The question whether the sparrow and the crocodile
have branched off from the same primitive form no more admits of a
philosophical answer, than does the question regarding the sparrow and the
hippopotamus.
284 MODEEN BIOLOGY
soul ; for God's almighty power cannot have produced the
soul, which is a spirit, out of matter, as it produced the forms
of plants and animals.1
No evolution theory is capable of bridging the gulf between
the mind of man and matter, which our experience teaches
us really exists. It is far greater than the gulf between in-
organic matter and organised substances, or than that between
vegetative and sensitive life ; its width is such that it will
never be bridged, just because mind and matter are diametri-
cally opposed. Modern monism has, of course, forgotten
this ancient truth, and is doing its best to ignore the essential
difference between them, but it is successful neither in the
mental physiology of man, nor in the comparative psychology
of man and beast ; between the movement of the atoms
in the brain and thought, between animal instinct and human
intelligence, yawns ever the old impassable gulf.2
Materialists are only wasting their time when they collect
stone after stone and fling them into the abyss ; the stones
vanish like dust in a bottomless pit, and the gulf remains
as wide as ever. Equally futile are all attempts to bridge
it by references to the ' intelligence ' of apes, or ants, or any
other animal, and by depreciating to the utmost extent the
1 In the Biolpgisches Zentralblatt for 1903, p. 602, note 1, Professor L.
Plate expresses his disapproval of this sentence, and criticises it as ' curious logic,'
adding : ' That God is almighty, and nevertheless is limited in His sphere of
action, is a contradictio in adiecto.' Has my good colleague never heard that
there are things which are not affected by God's omnipotence, because they
contain an interior contradiction ? Does he perchance fancy that God's omnipo-
tence could make 2x2 = 5 and not = 4 ? If so, he has a more exalted idea
of the divine omnipotence than all the theologians in the world put together.
— Have, pia anima !
2 A classical attempt to bridge this gulf was made by H. E. Ziegler in the
lecture already mentioned, ' Tiber den derzeitigen Stand der Deszendenzlehre in
der Zoologie.' On p. 28 he says : ' If the stag can be related to the roebuck,
in spite of the fact that the stag has large antlers and the roebuck only small
horns, so man can be related to beasts, although man has a great intellect
and beasts only a small one.' This profound statement deserves to be
inscribed in golden letters on the annals of comparative psychology, that
generations to come may benefit by it. One might almost fancy that it
was written at the time of shedding horns, when the old antlers of intellect
had been cast, and the new ones had not yet grown. Not long ago H. E.
Ziegler published a new treatise ' Uber den Begriff des Instinktes ' (Zoolog.
Jahrbiicher, Supplementary volume, VII, 1904, pp. 700-726), the historical
part of which abounds in superficialities and biased misrepresentations.
The author unfortunately gives a very poor account of instinct as it is usually
understood in Christian philosophy. It may be interesting to compare the
definition of instinct given in my book, Instinkt und Intelligenz im Tierreich,
1905, pp. 23, &c.
SCIENCE AND EVOLUTION 285
mental level of the wildest savages ; no success ever has
followed, or ever will follow, such attempts. The essential
difference between the mental life of man and the sentient
existence of beasts, and the impossibility that an alleged
brute ancestor of man should ever have become the first
homo sapiens by natural evolution, are facts that cannot be
set aside.1 Therefore, it is a real * postulate of sciencej to
account for the mind of man by an act of creation. This
involves no violation of the laws of nature ; for" as mind
cannot be produced out of matter, it is obvious that origin by
creation is, in the case of mind, the only natural mode of origin.
2. We have now completed our examination of the
philosophical limits to the theory of evolution and may
pass on to those assigned to it by natural science, although
here, too, we must begin with a philosophical preamble.
The theory of evolution is a scientific hypothesis, and in
its further development is a scientific theory. By an hypo-
thesis is meant a proposition, the truth of which cannot be
demonstrated directly by way of observation or experiment,
but which follows as a reasonable deduction from facts, because
it is capable of supplying a satisfactory explanation of them.
Hypotheses or suppositions are indispensable in natural
science ; without them there is in fact no science in this depart-
ment of knowledge, for science is scientia rerum ex causis ;
so, apart from hypotheses, we should have only a crass
empiricism, contenting itself with observations, and caring
nothing for the why and the wherefore of them. As our
immediate perception of the things of nature around us reveals
to us only their outer husk, our mind is forced to have recourse
to hypotheses, in order at least to some extent to be able to
penetrate into the working of the laws of nature. If various
modes present themselves of explaining one and the same
phenomenon or group of phenomena, the mind compares
and examines them to see which agrees best with the facts
that bear upon the subject, taken collectively. One is then
selected as the most probable hypothesis, which the student
of nature must accept, until a better is found.
1 On this subject cf. my two works, Instinkt und Intdligenz im Tierreich,
1905, and Vergleichende Studien uber das Seelenleben der Ameisen und der
hoheren Tiere, 1900.
286 MODEBN BIOLOGY
As an hypothesis obtains additional probability when
pieces of evidence from various sources concur to establish
it, it develops into a uniform scientific structure, and ceases
to be an hypothesis and becomes a theory. The nature of
things requires that we can never Jemalid such a degree
of certainty for a scientific hypothesis, or even for a theory,
as for a mathematical formula. Metaphysical (mathematical)
certainty can never exist with regard to it, and physical
certainty only seldom ; as a rule it can only claim a lower or
higher degree of probability. The Copernican theory supplies
us with an instance how an hypothesis, originally possessing
only a moderate degree of probability, may eventually rise
to the rank of a theory, having so much physical certainty
that at the present day no educated person doubts its accuracy.
It would be unfair to demand at the outset, in order to justify
the scientific existence of an hypothesis, that irrefutable
evidence in support of it should be adduced. To demand
this would be almost as foolish as, before partaking of any
food, to require a chemical guarantee that it contains no poison.
Let us now apply these principles to the theory of evolution.
The weight of the evidence in its favour is as often diminished
by exaggeration of its value on the part of its champions,
as by depreciation of its cumulative force on the part of its
opponents.
With regard to the nature and origin of the organic species,
we have to choose between two opposite theories, each of
which consists of a group of connected hypotheses. Of these
theories one, that of permanence, maintains the absolute
invariability of the systematic species. It is of opinion that
the species are perfectly unchangeable, although varieties and
breeds may be formed within them ; therefore it regards
relationship between the species as impossible, and as equally
impossible the suggestion that our present species can be the
descendants of other extinct ones. Consequently it assumes
so many special acts of creation to have been performed as
there are distinct systematic species, and we may assume
that at least 800,000 are known to exist now. But in the
various geological periods, as a rule, species have followed
one another, — they appear at the beginning of a period and
vanish at its close ; so that this theory requires the acts of
SCIENCE AND EVOLUTION 287
creation to have been constantly repeated during the whole
geological evolution of our earth. ' But why,' some one may
ask, 'need we lay so extreme an interpretation upon the
theory of permanence ? Why do we not rather say that it
requires a relative, but not an absolute, invariability of the
species ? ' Simply because to accept a merely relative per-
manence of the species involves necessarily the acceptance
of a relative variability. A theory of permanence, which
declares the systematic species to be ' relatively variable/
regards them as variable either only within the limits of the
species or beyond those limits. In the first case it asserts
practically the absolute permanence of the limits of the
species, and restricts the variability to the characteristic
marks of the varieties and breeds within the species ; in the
second case, on the contrary, it ceases to be a theory of per-
manence, for it accepts the principle of the theory of evolution,
which regards the systematic species as related by belonging
to a common stock. It must not be forgotten that the historic
strife between the theories of permanence and descent concerns
the systematic species in natural science, not the so-called
natural species. Our idea of the latter is based on natural
philosophy, and has taken its present form under the influence
of the theory of evolution. I shall have to recur to it in the
next section of this chapter.
Our second alternative is the theory of evolution, according
to which the organic species have been evolved from earlier
forms belonging to previous ages. It holds that the species
are relatively permanent for a definite geological period,
and that palseontological research shows shorter periods of
transformation to alternate with longer periods in which the
organic forms do not vary.1 We are now in one of the latter,
more permanent periods, and this explains the normal per-
sistence of our systematic species ; they correspond to the
conditions of life around them ; but as there is only a relative,
and not a fundamental difference between the characteristics of
1 Cf. Zittel, Grundzuge der Palaontologie, 1903, p. 15. Attention was drawn
to this phenomenon by Oswald Heer in his Urwelt der Schweiz, 1883, chapter
xviii. What de Vries calls the ' periods of mutation,' and the periods of
* explosive ' transformation of species (Koken, Standfuss), are only other
names for the above-mentioned periods of change. The view which de Vries
takes of his ' periods of mutation ' is extremely hypothetical (Mutations-
theorie, II, 1903, § 12, p. 697).
288 MODEEN BIOLOGY
species and of genera in systematics, this theory extends the
idea of a natural evolution also to the origin of genera. The
genera of systematic classification are only groups of natural
species, more closely akin to one another than to the species of
other groups, although they may originally have branched off
from the same stock. The theory of evolution affects families
and orders in the same way, and, as far as facts allow, also the
higher divisions of the animal and vegetable kingdoms. So
much for the theory.
What are the limits of the theory from the point of view
of natural science ? How far do facts enable it to answer the
three following questions, with which philosophy cannot deal ?
At what date did organic life begin? Must we assume the
evolution of plants and animals to have been monophyletic or
polyphyletic ? What internal and external causes gave rise
to the hypothetical race-evolution ?
We know very little as yet regarding the date when living
organisms first appeared upon our earth. It is certain that
life was possible only after the surface of the earth had
cooled down, and had formed an atmosphere about itself. The
earliest organisms probably lived in the water.1 In geological
language, the date of the first appearance of organic life
coincides with the end of the Azoic and the beginning of the
Palaeozoic age. The dividing line between these two periods
in the history of our planet must probably be set further back
than has hitherto been done. It is well known that geologists
used to regard the Cambrian formation as the oldest stratum
containing fossils. But recently Pre- Cambrian fossils have
been found in North America, Great Britain, Scandinavia,
Bohemia, and elsewhere, so that now the Pre-Cambrian is
regarded as the oldest stratum containing fossil remains of
living creatures.2 In the present state of our knowledge it is
still quite impossible for us to fix the age of this stratum ; very
likely millions of years have passed between the time when
it was formed and now.
1 Dependent on this is the further question whether the first centres of
creation were at the poles, i.e. at the ends of the shortest axis of the earth,
or in the equatorial zone, at the ends of the longest axis. On the latter
hypothesis see Simroth, ' Uber das natiirliche Sj'stem der Erde ' ( Verhandl.
der Deutschen Zoolog. Gesellschaft, 1902, pp. 19-42).
2 Cf. on this subject, Credner, Elemente der Geologie, 1902, pp. 389-394 ;
R. Hcrtwig, Lehrbuch der Zoologie, p. 151 (English translation, p. 180).
FOSSIL ANIMALS 289
We do not know whether the primitive forms of all the
creatures that lived later, of all classes in the animal and
vegetable kingdoms, existed in the Pre-Cambrian period. Prob-
ably they did not, for, as far as we know, vertebrates appeared
first in the Silurian, and flowering plants seem to be of still
later origin. Whether the occurrence of any particular class
of forms was really the first or not, is a point on which no final
answer can be given, and therefore, from the scientific stand-
point, we are still far from being able to decide whether the
primitive types of the chief classes of animals and plants were
produced simultaneously or in succession, nor can we say
when they first appeared.
I may here give a short sketch of what palaeontology
teaches us regarding the sequence of plant and animal forms in
the course of the earth's history. The list of the geological
strata with the names of the various formations has been
already given (p. 253), and I need not repeat it here.
In speaking of animals I shall follow chiefly Zittel's ' Grund-
ziige der Palaontologie,' and E. Hertwig's 'Lehrbuch der
Zoologie.' No living organisms can be assigned with certainty
to the Azoic or archaic age. The animal nature of the famous
eozoon found in the Archaean (Laurentian) strata is, to say the
least, very doubtful. The Palaeozoic age supplies the earliest
organisms. In the Pre-Cambrian strata of Brittany there are
numerous remains of Radiolaria, if Barrois is correct in his
interpretation of the discoveries made. The Cambrian strata
contain only remains of various classes of invertebrates,
amongst which Arthropods (Trilobites), Brachiopods (reckoned
by Hertwig among Worms), Echinoderrns and Molluscs are
the chief. In the Silurian, besides the above-mentioned, occur
the first vertebrates of the class of fishes, and the first insects
among the Arthropods. In the Devonian there are many
different kinds of fishes. In the Carboniferous begin the
Amphibia, and in the Permian the reptiles. In many cases
the forms of these palaeozoic creatures very closely resemble
those of the modern representatives of the same classes (Nauti*
lus, Lingula) ,but as a rule they are very different (e.g. Trilobites),
although frequently they are not inferior to their modern
relations in their degree of organisation. The Mesozoic age
is that in which reptiles reached their highest development,
290 MODERN BIOLOGY
and the insect fauna of the Lower Jurassic or Lias is very
numerous. The first mammals appear in the Triassic or
earliest Mesozoic age, and in the Upper Jurassic the first birds,
if we may reckon the Archaeopteryx as a genuine bird, in spite
of its many points of resemblance to a reptile. The fauna of
the Csenozoic age approaches more and more to that of the
present time ; in the Tertiary period the still existent orders
of mammals and birds developed, and the likeness between the
insects of that period and our own is still more striking. Man
appeared only in the Quaternary period, on the threshold of
modern times.
According to Eeinke's ' Philosophie der Botanik ' (pp. 132,
&c.) the geological sequence of plant-forms is as follows.
There are no remains at all of plants in the Pre-Cambrian and
Cambrian strata ; the earliest are ferns, which occur in the
Silurian, at the same time as the first land animals (insects). Of
other Cryptogams, the chalk-algae also occur in the Silurian, the
flint-algae in the Carboniferous strata, and they form enormous
deposits in the Chalk and Tertiary strata. Ferns, shave-grasses,
and Lycopodia reached the highest point of their development
in the Coal age, and had then in some ways a more perfect
organisation than at the present time. There are no fossils
that can serve as links connecting the Algae and the mosses,
or the mosses and the ferns.
The Gymnosperms were the first Phanerogams to make
their appearance. The earliest of them are the Cordaitae,
relations of the Cycadaceae, which appear first in the Devonian,
reach their highest point in the Carboniferous, and vanish in
the Permian. The first undoubted remains of Cycadaceae
occur in the Permian, as well as the first Ginkgos and Conifers.
In the Mesozoic age, in the Triassic, Jurassic and Cretaceous
periods, the three above-mentioned families of Gymnosperms
developed still further, and in the Tertiary strata occur only
such kinds as are still known. The earliest Angiosperms, both
monocotyledons and dicotyledons, appear suddenly in a great
variety of forms in the Upper Chalk, and are unconnected
with the Gymnosperms that preceded them. During the
Tertiary period more and more representatives occur of still
existent families, genera and species of Gymnosperms, and
their frequency increases in the more recent strata.
FOSSIL PLANTS 291
What information as to the hypothetical history of the
primitive forms in the organic world is given us by palaeon-
tology in its two branches, palseozoology and palaeophytology ?
It tells us nothing certain as to the date of the appearance
of the first living organisms or as to their structure, for those
organisms alone could be preserved as fossils which were
solid enough to make impressions or hollows in the stone ;
all soft protoplasmic formations must have perished and
left no trace. Moreover, it gives us only faint suggestions,
though they are extremely valuable, as to the order in which
the chief classes of animals and plants appeared upon earth,
but it affords certain evidence that the Fauna and Flora of
former ages gradually approximated more and more to those
of the present time. Numberless families and genera of
ancient animals and plants have become extinct, some long
ago, some more lately, leaving no descendants ; but on the
other hand very many seem to have been really the ancestors
of our present Fauna and Flora, in spite of the inevitable gaps
in the palaeontological records, and in spite of the uncertainty
still attaching to the interpretation to be put upon many
palaeontological discoveries.1
Let us now turn to the second question and ask : * Are
we to assume that the evolution of animals and plants was
monophyletic or polyphyletic ? ' There is no trace of any
scientific evidence to show that the two organic kingdoms
were descended from one common primitive cell. It is true
that now every multicellular organism in its ontogeny proceeds
from a unicellular stage, and among unicellular organisms
there are many of which it is impossible to decide whether
they are plants or animals ; but it is a very bold speculation
to conclude from these considerations that all organisms are
descended from a common ancestral cell. We are quite ignorant
too as to whether we must assume the vegetable kingdom and
the animal kingdom respectively to have had a monophyletic
or polyphyletic evolution. This alone is certain ; there is
no evidence at all in support of a monophyletic phylogeny.
" All honest supporters of the theory of evolution, who
1 Tn his book on the theory of descent (Die Deszendenztheorie) Fleischmann
has emphasised these two points as detrimental to the theory of evolution,
but he has exaggerated their importance. Cf. the discussion in Stimmen aus
Maria-Laach, LXII, 1902, Part I, pp. 116, &c.
u 2
292 MODEEN BIOLOGY
pay due attention to facts, acknowledge further that the
grounds for assuming the existence of a real relationship
between the forms in question become more scanty when
the higher divisions of the system are considered. For the
species of one genus these grounds often amount to great
and even irrefutable probability,1 and the same may be said
in not a few cases of the genera of one family, and occasionally
for the families of one order, but it can seldom be maintained
of the orders of one class. The evidence afforded by natural
science for the theory of common descent becomes steadily
weaker the higher we ascend in the system, and it becomes
weaker, too, the deeper we go into the palseontological history
of our earth in order to seek the common ancestors of the
subsequently distinct, systematic divisions.
In the latest (7th) edition (1905, p. 152) of his ' Lehrbuch
der Zoologie ' K. Hertwig gives the chief natural groups
of the animal kingdom as seven in number (Protozoa, Coelen-
terata, Worms, Echinodermata, Mollusca, Arthropoda, Verte-
brata) ; C. Glaus reckons nine, and the number is variously
given by other zoologists ; but the evidence in support of
the theory that these groups are of common origin is so weak
that we must describe it as improbable rather than probable,
in the present state of our knowledge. The truth of this
statement becomes apparent if the different hypotheses
be compared ; for instance, those put forward to account
for the descent of Vertebrata or of Arthropoda from other
groups of animals ; with regard to these hypotheses we might
almost say : Quot capita, tot sensus. When the opinions of
scientists diverge so greatly on one and the same point, we may
safely conclude that nothing certain is known about it. Whether
we accept seven or seventeen, or any other number, as that of
the chief types of the animal kingdom, it is always impossible
to assign to them a monophyletic descent from a common
primitive form. This has been thoroughly proved by Hamann
(' Entwicklungslehre und Darwinismus,' 1892), and by Pleisch-
mann (* Die Deszendenztheorie,' 1901) ; recently even Theodor
Boveri expressed the same opinion in his rectorial address
on May 11, 1906 (' Die Organismen als historische Wesen,'
Wiirzburg, 1906, pp. 7 and 51).
1 Instances of this will be given in Chapter X. See also pp. 276, &c.
MONOPHYLETIC OK POLYPHYLETIC EVOLUTION ? 293
The same holds good with regard to the chief classes
among plants ; R. von Wettstein thinks that we must dis-
tinguish seven, all independent of one another (' Handbuch
der systematischen Botanik,' I, 1901, p. 16).
In fact, among modern zoologists and botanists, and still
more among palaeontologists,1 the number is ever increasing
of those who think that the evolution of both animals and
plants was polyphyletJCj and who regard the monophyletic
hypothesis as merely a pretty fancy on the part of the supporters
of the theory of descent in its crude form — a fancy that they
cannot hope to prove true, for comparative morphology and
ontogeny of living organisms, as well as the discoveries made
by paleontology, all alike render it more and more improbable
that anyone will ever succeed in establishing a monophyletic
evolution of either the animal or the vegetable kingdom on a
scientific basis. It becomes more and more probable that
anionophyletic evolution does not correspond at all with
facts.
"~No serious student is at present able to tell us with cer-
tainty how many independent lines of descent, or series of
evolution, we must assume to exist among animals and plants
respectively. This is due partly to the fact that the answer
to this question depends greatly upon the subjective ideas
of each individual, but the chief reason for it lies in the signi-
ficant circumstance that a final answer will be possible only
when we have a perfect knowledge of both the present and
the fossil organic world. At the present day we are at an
immense distance from possessing such knowledge, and there-
fore we do not know how many original acts of creation must
be assumed, in order to account for the existence of the living
organisms in the world. Koken says on this subject (1902,
p. 218) : ' All the great Phyla go back, sharply distinguished,
to the Cambrian period, and we have no records at all of
those periods when they might have been connected, or when
they branched off from a common stock.' Steinmann (1899,
1 Cf. on this subject. E. Koken, Die Vorwelt und ihre Entwicklungsgeschickte,
Leipzig, 1893 ; ' Palaontologie und Deszendenzlehre,' address given at the
seventy-third meeting of German naturalists at Hamburg, on September 26,
1901 (Verhandl. I, Leipzig, 1902, pp. 212-228. Reprinted Jena, 1902). G.
Steinmann, Die Erdgeschichtsforschung wdhrend der letzten vier Jahrzehnte
(Freiburg i. B., 1899); Palaontologie und Abstammungslehre am Ende des
Jahrhunderts (ibid., 1899).
294 MODEKN BIOLOGY
p. 33) goes so far as to believe that men will never attain to
this knowledge : ' I feel certain that the oldest representatives
of animals and plants of every kind will for ever remain un-
known to us ; all trace of them has probably vanished, owing
to the great changes undergone by the oldest strata.'
We still do not know, and probably we shall never know,
under what form we are to imagine the hypothetical primitive
types of the various series of evolution ; whether we are to
think of them as very simple cells, having however an already
definite tendency or Anlage to evolution ; or as phylembryos,
or as further differentiated forms, displaying the exterior
characteristics of the various types in the shape of definite
morphological designs. Nor can we state anything as to the
appearance of these primitive types ; we do not know whether
they all appeared at the same time, or in succession, nor when
they were produced.
We come now to the third question : * What does natural
science tell us of the interior and exterior causes of the
hypothetical race-evolution ? ' Here we are still more com-
pletely in the dark. Leaving aside those prejudiced persons
who are blindly in love with their own theory — the theory
of selection, or orthogenesis, or whatever it is — and fancy
that it explains everything (although, as a matter of fact, it
explains very little), we may frankly acknowledge that our
knowledge of the reaL causesof the_^ac^e-evolution_Qf the
organic species is still in itslrjiaiic£^0ne thing alone seems to
be fairly^ certain : Numerous interior and exterior factors
must be regarded as the causes of the race-evolution, and
the part played by these factors with respect to various series
in evolution differs greatly as to the extent both of their
participation and co-operation.1
Just as, in the development of the individual organism, pre-
formation and epigenesis work together in accord,2 and definite
interior tendencies are regularly modified by exterior influ-
ences, so, as we may suppose, is it in the race-evolution of
living organisms. In general we must follow Nageli in dis-
tinguishing, in the case of organic species, characteristics due
1 Some instances taken from zoology will be found in Chapter X.
2 See Chapter VIII, p. 225, and p. 235. Also 0. Hertwig, Allgemeine
Biologie, 1906, pp. 132, &c., pp. 138, &c.
PROBLEMS AWAITING SOLUTION 295
to organisation from those due to adaptation. The former,
which determine the degree of organisation, must primarily
be referred to the interior causes of evolution, whilst the
latter are connected with the influence of the, exterior causes.
The active parts taken by both series of causes are more or
less mixed, and the interior causes are always the foundation,
acted upon by the exterior (e.g. nutrition, temperature, light,
&c.), which affect evolution by means of various attendant
stimuli.1
I cannot at present discuss this topic further. I have
considered both the philosophical and the scientific limitations
of the theory of evolution, and, as I believe, have dealt
impartially with both philosophy and science. We must
not undervalue, but neither must we overvalue, the achieve-
ments of the theory of evolution hitherto. Centuries
will pass before it succeeds in establishing, with a sufficient
degree of probability, the number of primitive series of animals
and of plants respectively, and in arranging correctly the
forms belonging to each series in the many ramifications of
their relationship. Centuries more must elapse before science
will be able to trace back these series to their origin, and to
discover the primitive forms of each. And centuries of research
will be required before men will find a satisfactory explana-
tion of the causes which control evolution within each series
of forms. Shall we therefore be contented to say : * Before
we acknowledge the theory of evolution to have a scientific
justification, we had better wait until it has accomplished
all these tasks ? ' To do so would be both unreasonable
and foolish. On the contrary, we can only wish that as many
serious research-students as possible may apply themselves
with all zeal to solving the difficult problems connected with
the theory. This solution could not fail to benefit philosophy,
whilst it would be far more creditable to the theory of evolution
for its supporters to proceed thus, than to act like Haeckel and
those who share his opinions, and try to popularise the theory
1 Cf. also p. 176 and p. 282 ; also B. von Wettstein, Berichte der botanischen
Gesellschaft, XVIII, 1900, pp. 184-200 ; E. Koken, Paldontologie und Deszendenz-
khre, 1902 ; Ed. Fischer, ' Die biologischen Arten der parasitischen Pilze
und die Entstehung neuer Formen im Pflanzenreich ' ( Verhandl. der Schweizer
Naturforschergesellschaft, eighty-sixth annual meeting, Locarno, September
1903) ; Uber den heutigen Stand der Deszendenzlehre und unsere Stellung zu
derselben, Berne, 1904.
296 MODEKN BIOLOGY
to advance their own ends, and make a wrong use of it as
a weapon with which to attack the Christian cosmogony.
6. SYSTEMATIC AND NATUBAL SPECIES
Linnaeus, who is to be regarded as the originator of our
present conception of systematic species, and who, therefore, has
been called the father of the theory of permanence, enunciated
the following dictum : Tot species numeramus, quot diversae
formae in principio sunt creatae — we reckon so many (syste-
matic) species as there were different forms created in the
beginning.
How must this dictum be worded to make it agree with the
theory of evolution ? According to it, the systematic species
of the present time do not represent the originally created forms,
but are the result of a process of evolution, uniting the species
of the present and the past in natural series of forms, the
members of which are related to one another, and each of
which points back to an original primitive form, whence it
is derived. If we designate each of these independent series
of forms, not related to other series or families, as a natural
species,1 we can still assent to Linnaeus's dictum : Tot species
numeramus, quot diversae formae in principio sunt creatae. We
reckon so many natural species as there were different primitive
forms created in the beginning.2 Each of these natural species
1 A similar view regarding natural species has already been expressed
by Father T. Pesch in his Philosophia naturalist, II, p. 334, in order to explain
the facts supporting the theory of evolution. He quotes a number of passages
from St. Thomas Aquinas and from Suarez in favour of his view. Of course
we are here speaking of the species physicae of natural philosophy, not of
the species metaphysicae of logic. Almost inconceivable mistakes as to my
definition of natural species have been made by many reviewers of the first
edition of this work, some of them being experienced zoologists. Escherich
in the Supplement to the Allgemeine Zeitung for February 10, and 11, 1905,
gave it far too narrow an interpretation, and Haeckel, Forel and others simply
followed him and made the same mistake, without examining the matter
for themselves. Another mistake was made by Friese (Wiener Entomologische
Zeitung, 1904, No. 10) and Schroeder (Zeitschrift fur wissenschaftl Insekten-
biologie, 1905, Part 4), who believe my distinction between systematic and
natural species to be identical with that between biological and morphological
species ; the biological and the morphological species are but two different
aspects of the systematic species, whilst the natural species comprises all
the members of the same line of ancestry or pedigree, and therefore is much
wider from the point of view of natural science. I trust that these remarks
will prevent further misunderstandings.
2 For readers who have studied philosophy, it is perhaps needless to remark
again (as I do for the benefit of some of my critics), that the creation of the
SYSTEMATIC AND NATURAL SPECIES 297
has in the course of evolution differentiated itself into more
or less systematic species. How many systematic species,
genera, and families belong to a natural species, cannot yet be
stated with certainty in most cases. Still less are we able
to say how many natural species there are, i.e. how many lines
of ancestry independent of one another. We must leave the
decision to the phylogenetic research of future ages, if indeed
it ever succeeds in arriving at one.
The varying degrees of capacity for evolution possessed
by the primitive forms of the different natural species depend
primarily upon the interior laws of evolution impressed upon
their organic constitution ; we are probably justified in
regarding the chromatin substance of the germ-cells as the
material designed to transmit these laws.1 The interaction of
these interior factors in evolution and of the surrounding
exterior influences, through which many kinds of adaptation
came about, have produced the ramifications from the parent
stock of the natural species, and they have been affected also
by cross-breeding (amphimixis) and natural selection.
But, it may be asked, what is the practical advantage of
distinguishing thus natural and systematic species, if we are
still unable to determine which forms actually constitute a
natural species, and how many such natural species there are ?
To this question we may answer : Firstly, in many cases we
are able at the present day to decide in some degree the group
of forms which belong to a natural species, although we may
not yet know with certainty its full extent* For instance we
may reckon, as belonging to one natural species, all the varieties
of beetle of the Paussidae family, from the Tertiary period
to the present time ; 3 but as the Paussidae, even if they are
the outcome, not of a monophyletic, but of a diphyletic
evolution (cf. Chapter X, § 9), are related phylogenetically to
first organisms is not to be understood as a creatio e nihilo, but as a production
of organisms out of matter. On this subject see the sections on Spontaneous
Generation (p. 193), and on the Philosophical Limitations of the Theory of
Evolution (p. 279).
1 See Chapter VI, p. 169 and p. 177, &c.
2 I have italicised these words because they were overlooked by Escherich
and other reviewers in the former edition.
3 Cf. Stimmen aus Maria-Laach, LIU, 1897, pp. 400 and 520, &c., ' Die
Familie der Paussiden' ; also 'Neue Beitrage zur Kenntnis der Paussiden mit
biologischen und phylogenetischen Bemerkungen ' (Notes from the Leyden
Museum., XXV, 1904).
298 MODEKN BIOLOGY
the Carabidae, and these again to other families of beetles, the
real extent of the natural species in question is probably much
greater. With still greater certainty may all the varieties
of Staphylinidae belonging to the group Lomechusa be regarded
as forming a natural species. We may therefore rightly say :
All the Lomechusini form one natural species and not more
than one. But we do not mean to limit the extent of this
natural species to the Lomechusini) for this group of Staphylinidae
is connected phylogenetically with other groups of the same
family, and the whole family of Staphylinidae with other families
of beetles, &c.
If we consider the numerous genera and species of ants
from the earliest Jurassic period to the present day, we can
hardly doubt that they are offshoots of one single natural
species, and are not several natural species. The same remark
applies to the family of termites, with its great variety of fossil
and still existent genera and species.1 If we trace back
the history of the primitive varieties of the Palaeozoic age,
which even then formed several distinct classes, whence our
present orders of insects branched off probably in the Mesozoic
age,2 we may succeed perhaps, in course of time, in proving
these varieties of primitive insects to be offshoots of some
original stock, which possibly is connected with the earliest
marine Arthropoda, so that eventually many hundreds of
thousands of systematic species may unite to form one single
line, one single natural species.
This is at present all a matter of pure hypothesis ; but
these examples serve to show plainly that the limits to be
assigned to the natural species become more and more uncertain
the higher the division of the animal system and the more
remote the historical period of animal life under consideration.
It will therefore be best for practical purposes to describe as
natural species only those groups of forms which investigation
has shown with sufficient probability to be uniform genealogical
series.
Thus, for instance, we may class as one natural species all
the present varieties of horse (Equidae) and their fossil ancestors,
comprising various systematic genera, although we do not
1 See p. 276.
2 Cf. A. Handlirsch, Die fossilen Insekten, Leipzig, 1906.
SYSTEMATIC AND NATUKAL SPECIES 299
yet know how far the limits of this natural species may be
extended into the past of which palseontology takes account.1
Among Molluscs, the Ammonites may be mentioned as a
group of forms very rich in systematic families, genera, and
species ; they can be traced from the Devonian to the Cretaceous
period through a long series of geological strata, as a uniform,
close line of forms, that we must reckon as all belonging to
one natural species, not to many. I might add many other
instances, but those already given will suffice to show that
the distinction between systematic and natural species is by
no means devoid of actual foundation. It is in fact practically
necessary, if we are to have a scientific knowledge of com-
parative morphology and biology.3
Secondly : The distinction is of far greater importance from
the point of view of philosophy. It supplies us with a firm
philosophical basis, upon which the theories of creation and
descent can easily be reconciled with one another. It is
obvious that the possession of such a basis is of the utmost
importance to those concerned with the defence of Christi-
anity. Our monistic opponents are fond of adopting the
device of directing their attacks against the theory of per-
manence, when they are really aiming them at the theory
of creation. They declare the two theories to be identical,
and hope, by overthrowing the one, to secure the downfall
of the other. But their hopes are doomed to disappoint-
ment, if we resolutely maintain the distinction just laid
down. If we believe that only the natural species in their primi-
tive forms were created, but that it is left to natural science to
determine the number and extent of these series of natural forms,
as well as the character of the primitive forms themselves, then
the enemies of the Christian cosmogony will no longer be able to
taunt us with having to accept the permanence of the systematic
species as an article of faith.3 What has it to do with theistic
cosmogony whether a hare and a rabbit, a horse and an ass
are related or not ? The recognition of a personal God, the
1 Fleischmann's criticism of ' the stock instance of the theory of descent '
(Die Deszendenztheorie, chapter v) seems only to confirm the above statement,
and not to prove much against the relationship of the Equidae to one another.
2 Further information on this subject, derived from my own investigations,
will be found in the next chapter.
3 This italicised passage gives the reason for the bitter attacks made by
monists upon the ' natural species.'
300 MODEKN BIOLOGY
Creator of all finite beings, is no more inseparably connected
with the theory of permanence in zoology and botany than
it was with the geocentric system in astronomy.
If the theory of descent holds its ground, and takes the place of
the old theory of permanence, the theory of creation, and with
it the Christian cosmogony, remains as firmly established as ever.
Indeed the Creator's wisdom and power are revealed in a more
brilliant light than ever, as this theory shows the organic world
to have assumed its present form, not in consequence of God's
constant interference with the natural order, but as a result
of the action of those laws which He Himself has imposed upon
nature.
We see therefore that, in this department also, true science
leads us finally to a fuller recognition of God.1 It is a mere
delusion on the part of modern atheism, in its various forms
and shades of opinion, to fancy that the theory of evolution
has enabled the world to dispense with a Creator ; for, the
more manifold and the more independent is the evolution of
the organic world according to the laws inherent in it, the
greater must be the wisdom and power of the law-giver who
created this world. The Darwinian, or rather Haeckelian,
theory of chance, which derives all the conformity to law in
nature from an original lawless chaos, by means simply of ' the
survival of the fittest,' may at the present day be said to be
discarded by science. But the monistic view of the universe,
which professes to find the first cause of the orderly arrangement
of the world in the world itself, and not in a personal Creator
substantially distinct from it, is no better than the material-
istic theory of chance ; for the so-called God of monism, whom
it identifies with tho world and everything therein, proves to
be a true medley of irreconcilable and inexplicable contra-
dictions, when considered in the light of sound reason. We are
told that God is the most perfect being, having from all eternity
the ground of His existence in Himself ; but at the same time
He is a God who must develop His own being in and through
the world. Such a monistic God would be pitiably incomplete
and dependent, for His very existence would depend upon the
1 On this subject see K. Braun, fiber Kosmogonie vom Standpunkt christlicher
Wissenschaft, 1905, especially chapters 8 and 9. Also J. Reinke, ' Darf die
Natur uns als Offenbarung Gottes gelten ? ' (Turmer Jahrbnch, pp. 139-167,
especially pp. 162, &c.).
GOD THE CREATOR 801
existence of every midge, and fly, and creature in which
He develops Himself. To have invented such an idea of God
and to seek to make it take the place of the theistic conception
of Him, are achievements of modern lack of thought, not o
modern science. But, on the contrary, the recognition of a
personal God, who, in virtue of the fulness of His own being,
created the world out of nothing, is still demanded by sound
human understanding, and is therefore a true postulate of
science.1 Although God is present and acts in all His creatures,
He is essentially distinct from the world and independent of
it, and has shone forth from all eternity with the same un-
changing purity and perfection. All the ephemeral deities
of modern monism must give way to this only true God of
Christianity.
At the present day men are fond of attacking the theistic
cosmogony by saying it is an ' untenable dualism ' to recognise
a God as essentially distinct from the world. Nobody has
yet proved this dualism to be untenable, though monism
certainly is so. I am not one of those who ' prefer the most
pitiable confusion to dualism ' (C. Stumpf). There is in
reality onlyone true kind of monism, and that is the unity.
oMhelirst Tause 5f_all rniit^Jbejng^^od in His infinitjT2
People are tond of quoting (Jharles Darwin as an authority in
support of the modern theory of evolution, but he did not
feel that blind hatred of the Creator which characterises
Haeckelism. Although we know from some of his later state-
ments that he inclined to agnosticism, he never altered the
closing words of his chief work, the ' Origin of Species.' Even
in the sixth edition, published in 1888, after his death, this
beautiful passage occurs : ' There is grandeur in this view
of life, with its several powers, having been originally breathed
by the Creator into a few forms or into one ; and that, while
this planet has gone cycling on according to the fixed law
1 The accounts of the theory of creation given in modern scientific works
are most inadequate. See, for instance, Lotsy's Vorlesungen uber Deszendenz-
theorie, I, 1906, pp. 5-8. Lotsy there rejects the atheistic and the pantheistic
hypotheses regarding the origin of the world, but professes himself unable to
accept the theistic view, which he seems to prefer, because « the idea of self-
existence is absolutely unintelligible.' This is true only of those who have
never opened a book on Christian theodicy.
2 Cf. the third edition of my work on Instinkt und Intelligenz im Tierreich,
1905, p. 276.
302 MODEKN BIOLOGY
of gravity, from so simple a beginning endless forms most
beautiful and most wonderful have been, and are being evolved.'
Very similar is the opinion expressed by Lyell, the great
geologist, in writing to Charles Darwin, on March 11, 1863.
He maintains that the acceptance of a phylogeny of the
organic species by no means enables us to dispense with the
idea of creation. ' I think,' he says, ' the old " creation "
is almost as much required as ever, but of course it takes a
new form, if Lamarck's views, improved by yours, are
adopted.' l
7. SUMMARY OF KESULTS
Before I pass on to a closer comparison between the
theories of permanence and descent, it will be well to arrange
the results at which we have arrived under different headings.
This is the more necessary, as various reviewers of the first
edition have given an unfair account of the contents of this
chapter.
Our consideration of the theory of evolution has shown
that :—
(1) Darwinism and the theory of evolution are two quite
different things, which ought not to be confused with one
another. Darwinism in the narrower sense of the word is
Darwin's theory of selection ; in . the wider sense it is the
generalisation of that theory to a so-called Darwinian
cosmogony.
(2) Darwin's theory of selection cannot be the chief factor
in any hypothetical race-evolution, because it merely accounts
for the extirpation of the unfit, and not for the development
of the fit ; only a theory of evolution, ascribing due importance
to the interior causes of evolution, can possibly succeed in doing
the latter. The Darwinian cosmogony must be rejected
absolutely.
(3) The doctrine of evolution, as a scientific hypothesis
and theory, aims at investigating the successive forms of
animals and plants that have existed from the earliest Palaeo-
zoic age to the present time, and at discovering their causes.
1 See Francis Darwin, Life and Letters of Charles Darwin, II, London, 1888,
p. 193.
SUMMARY OF RESULTS 303
It is not an empirical science, but it strives to give a uniform
account of the facts observed in biology.
(4) The chief philosophical points to be observed in dealing
with the theory of evolution are : (a) We must assume the
existence of a personal Creator as the first exterior cause of the
origin of matter and of life ; (b) We must believe that a X,
special act of creation on God's part was required for the
production of the mind of man ; (c) Finally, we must acknow-
ledge interior laws of evolution to be the chief causes of an
orderly race-evolution.
(5) The following points may be regarded as settled with
regard to the scientific aspect of a hypothetical race-evolution :
(a) There is no scientific evidence at all in support of a mono-
phyletic origin of all living things from one single primitive
cell ; (b) A monophyletic evolution of the animal kingdom
on the one hand, and of the vegetable kingdom on the other,
appears very improbable, when the results of palaeontological
research are taken into consideration ; but the scientific
evidence in favour of a polyphyletic evolution of animals and
plants is steadily gaining weight. We may therefore accept
the polyphyletic evolution of both animals and plants from
the standpoint of biology and palaeontology alike ; but the
number of the various lines of descent, and the extent of each,
are still very obscure.
(6) Equally obscure, from the scientific point of view,
are the causes of this hypothetical race-evolution. We can
only say that probably many interior and exterior factors
co-operate in various ways to produce it, and that the interior
laws of evolution have always been the chief cause.
(7) If we call each of the hypothetical and distinct lines
of evolution in the organic world a ' natural species,' we may
say : ' There are as many natural species as there were originally
different primitive forms, produced at the creation of the
organic world.' We must leave it to future biologists to
determine the number and extent of these natural species,
and the structure of their primitive forms.
(8) As we have viewed it, the doctrine of evolution as a
scientific hypothesis and theory is perfectly compatible with
the Christian cosmogony. The ideas of creation and evolution
are not antagonistic, but the creation of the primitive forms
304 MODEKN BIOLOGY
is the natural basis of the subsequent phylogeny of the organic
world. Both together make up a theory of nature founded on
Christianity.
(9) What must we think of the theory of evolution as
a theory of the universe from the standpoint of the philosophy
of nature ? The view adopted by monism is wrong and
full of contradictions, for it excludes creation and upholds
nothing but evolution. But the view adopted by Christian
theism is right and logical, for it accepts God's creative action
as the starting point for the evolution of the organic world, and
then leaves it to natural science to establish the details of
that hypothetical evolution.
(10) We must once more carefully distinguish between
the scientific theory of evolution, and its philosophical generali-
sation into a cosmogony founded on Christianity. The former
is still a modest little plant, just raising its head above the
ground. The latter is a tree, stretching its branches far and
wide, and lifting its top to the clouds, but, as we must never
forget, its roots are still embedded to a great extent in philo-
sophical speculations, and not in scientific facts. If we bear
this distinction in mind, we may calmly assert : —
The Christian cosmogony, that accords with the theory of
evolution, reduces the history of animal and vegetable life upon
our planet (though it covers hundreds of thousands of years)
to a mere line in the book of the natural evolution of the whole
cosmos ; but on this book's title-page stands written in indelible
characters :
' In the beginning God created the heaven and earth.'
In the following chapter I propose to make use of facts
as the groundwork for a comparison between the theories
of evolution and permanence — a comparison which, as our
present survey of the theory of evolution necessarily suggests,
will result in our accepting the former and rejecting the latter.
CHAPTER X
THEOKY OF PERMANENCE OR THEORY OF DESCENT
(See Plates III-V)
1. ARGUMENTS FOR THE FIXITY OP SYSTEMATIC SPECIES.
Species form morphological and biological units (p. 307). Refutation
of Plate's views regarding the unlimited variability of organic
forms (p. 309).
2. DIRECT EVIDENCE IN SUPPORT OF THE THEORY OF EVOLUTION.
Mutation and cross-breeding as factors in forming new species (p. 312).
Among animals the breeds produced by artificial selection afford no
evidence that new species are now in course of formation (p. 314).
3. THE EVOLUTION OF THE FORMS OF Dinarda.
The parti-coloured Dinarda ' species ' are forms resulting from adaptation
to various kinds of guest -ants (p. 318). This process of adaptation
is not yet concluded. Dinarda pygmaea, D. Hagensi (p. 319).
Breeds of Dinarda giving rise to fresh species (p. 321). Extension
of these results to the connexion between Dinarda and Chitosa
(p. 322). Conclusions (p. 325).
4. INDIRECT EVIDENCE IN SUPPORT OF THE THEORY OF EVOLUTION.
Evidence derived from the comparative morphology and biology of
inquilines amongst ants and termites (p. 327). Various causes of
evolution (p. 328). Evolution of inquilines amongst ants and
termites considered from the palseontological point of view (p. 329).
5. HYPOTHETICAL PHYLOGENY OF THE Lomechusa GROUP.
Three genera of Lomechusini and their guest-ants (p. 330). The Lome-
chusini are to be regarded phylogenetically as a breed produced by
the ants' instinct to entertain their guests ; secondary adaptations to
Myrmica and Camponotus (p. 331). Division of the genera Lome-
chufa, Atemeles, and Xenodusa by adaptation to three different
genera of ants (p. 333). Division of the species within the genus
Atemeles by adaptation to various species and breeds of the genus
Formica (p. 334). Atemeles pratensoides as an instance of adaptation
resulting in the formation of species (p. 335). Supposed primitive
form of the Lomechusini and the laws of their evolution (p. 337).
Amical selection versus natural selection (p. 339).
6. INQUILINES AMONG THE WANDERING ANTS.
Resemblances between different genera of the mimetic type depend upon
analogous conditions of adaptation (p. 340). These phenomena
explained by the theories of permanence and evolution respectively
(p. 342). Comparison between the Dorylinae inquilines of the mimetic
type and of the offensive type (p. 344). Comparison between the
Eciton and the Atta inquilines (p. 345). Remarks on the laws
governing this evolution (p. 347).
305 x
306 MODEKN BIOLOGY
7. TRANSFORMATION OF WANDERING ANTS' INQUILINES INTO TERMITE-
INQTJILINES.
A termitophile species of Doryloxenus in the East Indies (p. 349).
Hypothetical explanation of this phenomenon (p. 350). Confirma-
tion and extension of this hypothesis by recent discoveries (p. 352).
Termitophile Doryloxenus, Discoxenus,a,nd Termitodiscus (p, 353). A
new termitophile Pygostenus in Africa (p. 357). Deductions affecting
the theory of evolution (p. 359).
8. THE FAMILY OF Clavigeridae.
Adaptation of their characteristics to their circumstances as inquilines
(p. 360). All the differences between the Clavigeridae and the
Pselaphidae prove on examination to be characteristics due to
adaptation (p. 361). The Clavigeridae are phylogenetically derived
from the Pselaphidae (p. 362).
9. THE HYPOTHETICAL PHYLOGENY OF THE Paussidae.
They are distinguished from the Carabidae by modifications due to
adaptation to their myrmecophile way of life (p. 365). The four
chief groups of Paussidae with different numbers of joints in their
antennae (p. 365). The genus Paussus as the ideal culmination of
morphological and biological evolution among the Paussidae (p. 367).
Did such an evolution really take place ? (p. 367). Some details of
this hypothetical phylogeny (p. 368). Evolution of four indepen-
dent branches from one original stock (p. 369). Was the evolution
of the Paussidae monophyletic or diphyletic ? (p. 372). Causes of the
hypothetical race-evolution. Interior capacity for transforma-
tion possessed by the primitive types (p. 373). Abrupt and
gradual evolution (p. 373). Exterior factors in transformation
(p. 374). Adaptation to ever higher degrees of guest- relationship
the chief motive for this evolution (p. 374). Differentiation of the
antennae within the genus Paussus (p. 375). Its biological significance
(p. 375). Natural selection unable to account for the diversity in
shape of the antennae (p. 376). Interior causes of this diversity
(p. 377). Exterior causes in amical selection (p. 379).
10. THE Termitoxeniidae, A FAMILY OF DIPTERA.
Their morphological, biological, and phylogenetic peculiarities (p. 380).
Explanations of these peculiarities offered by the theories of perma-
nence and descent (p. 381). The Termitoxeniidae must be regarded
as having been formerly true Diptera, whose structure, ontogeny,
and mode of propagation have been completely altered in consequence
of adaptation to the termitophile way of life (p, 382). The appen-
dages on the thorax of Termitoxeniidae an evidence of their evolution
(p. 384).
11. THE HISTORY OF SLAVERY AMONGST ANTS.
(a) Survey of the Biological Facts connected with it.
Nine groups of facts. Simple colonies of ants (p. 391). Temporarily
mixed adoption colonies (p. 392). Permanently mixed colonies due
to raids made by slave-keeping ants (p. 394). Various degrees of
the slave-keeping instinct and its culminating point (p. 397).
Parasitic degeneration of the instinct (p. 406). Permanently mixed
colonies of parasitic ants with no workers (p. 408).
(6) Inferences respecting the Development of the Slave-making Instinct.
This development is not to be regarded as belonging to one
real line of descent, but to many, all independent of one
another (p. 411). The development of the slave-keeping instinct
began at different periods among different genera and reached
various stages (p. 413). Genealogy of the slave-keeping
instinct. The causes of its development (p. 417). Its significance
in the formation of new species and genera of ants (p. 424).
PEEMANENCE OF SPECIES 307
12 CONCLUSIONS AND RESULTS.
The theories of permanence and descent compared with regard to their
value in supplying explanations (p. 426). The latter alone can
suggest natural causes to account, for the occurrence of expedient
adaptations (p. 427). It reveals the Creator's wisdom and power
more strikingly than does the theory of permanence (p. 429).
IN the previous chapter I suggested some thoughts on the
doctrine of evolution, which made it clear that there is a
great difference between Darwinism and the theory of evolution,
and threw considerable light on the latter from various points
of view. I drew especial attention to the connexion between
the Copernican system and evolution on the one hand, and
between evolution and the theory of creation on the other.
Let us now proceed to examine more closely the facts belonging
to the theories of permanence and descent. On account of
the enormous extent of the scientific evidence at my disposal,
I shall limit myself to a few instances derived from my own
branch of research, so that I am not dependent upon any
extraneous authority.
1. ARGUMENTS FOR THE FIXITY OF SYSTEMATIC SPECIES
At first sight the great majority of facts in zoology and
botany appear to support the permanence of the systematic
species. This theory stands in the same advantageous position
as the Ptolemaic system did long ago, for it too could adduce
almost all our own observation of nature as testimony in
its favour. Even at the present day, it might be a difficult
task to convince an ignorant country lad that -the sun is
stationary and -that the earth moves round it, because the
evidence of his own eyes is to the contrary, and the scientific
proofs are beyond his comprehension. It may well be that
the theory of evolution is now faring as the Copernican theory
did of old. Apparently most of the phenomena in the organic
world are against it, and therefore, unless we study the matter
closely and test carefully the scientific circumstantial evidence
in its favour, we run the risk of arriving at a decision such
as the country lad would form.
Even the adherents of the theory of evolution, when they
take facts sufficiently into account, confess more or less
frankly that the systematic species forms at the present time
x 2
808 MODEKN BIOLOGY
a morphological and biological unit. It is a morphological
unit, inasmuch as it is a group of individuals, the members
of which agree in the so-called ' essential ' characteristics,
and are regularly marked off from other groups of indi-
viduals. It is a biological unit, inasmuch as this group of
individuals constitutes a genetic whole, repeating through
an unbroken series of generations the same regular cycle of
forms, in the phenomena of embryonic development, meta-
morphosis and metagenesis ; and, further, where sexual
intercourse takes place, the members of one species can copulate
with one another, but not with those of another species, if
their union is to be fertile.1
These facts can be denied only by those ardent partisans
who, in discussing the doctrine of evolution, care more about
maintaining their theory than about giving it an objective
foundation. By far the greater number of the systematic
species of the present animal and vegetable kingdoms, and
most of the fossil species too, represent real morphological
and biological units, and this fact is generally recognised.
In the case of the fossil forms, it is of course impossible to
offer direct evidence in support of the biological unity of the
species, but it can be deduced from the morphological
unity. The organic world of the present, like that of the past,
is not a disorderly chaos of minute variations, such as the
Darwinian form of the theory of descent would require, with
its quite gradual and imperceptibly minute shades of difference
(for their average biological unimportance would prevent
the ' Struggle for Existence ' from ever arranging them in
well-defined groups of forms), but it is an orderly system
of species, genera, families, orders, classes, and groups. To
attempt any further proof of this is quite superfluous, for every
student of systematics knows it as a fact, which we may and
must assume to be generally recognised. Abundant informa-
tion on this subject may be found in any textbook of zoology,
botany, or palaeontology ; and therefore it is the more sur-
prising that many over-zealous advocates of the theory of
descent seem still to be completely unaware of it.
1 This last characteristic is not universally applicable ; among plants the
majority of the hybrids produced by crossing different species are fertile.
Cf. J. Reinke, Einleitung in die theoretische Biologie, 1901, pp. 536-537.
GOOD AND BAD SPECIES 309
Professor L. Plate,1 for instance, in a review of Fleischmann's
book on the theory of descent, published in the ' Biologisches
Zentralblatt,' says : ' The experience of systematists teaches
us, as plainly as we can possibly desire, that a species cannot
be sharply denned, because variability is a fundamental
phenomenon in organic life.' The testimony of actual facts
is directly opposed to Plate's statement. Without fear
of contradiction we may make the following assertion : ' The
experience of systematists teaches us as plainly as we can
possibly desire, that species are generally sharply defined,
because variability in organic forms is mostly confined within
the limits of the species.' In his zealous defence of the theory
of descent against Fleischmann's attacks, Plate has repre-
sented what is actually the exception as the rule, and
what is actually the rule as the exception. There are,
of course, what are called ' bad species,' connected
with one another by varieties, but it is precisely for
that reason that we call them bad, and contrast them
with the ' good species/ which are marked off from one
another by constant characteristics, and show no transitional
forms.
It would be better not to call these ' bad species ' by the
name of species at all, but to designate them rather as
sub-species or breeds, and to limit the idea of systematic
species to the sharply defined ' good species.' This, for
instance, is the reason why all the more recent scien-
tific writers, who have dealt with the classification of ants,
have followed Forel (1874), and divide them into species,
subspecies (or races), and varieties. Only in this way can
we succeed in grouping the forms systematically, so as to
1 ' Bin moderner Gegner der Deszendenztheorie ' (Biolog. Zentralblatt, XXI,
1901, Nos. 5 and 6). The passage quoted occurs on p. 142. It is hardly
necessary to remark that I do not agree with Fleischmann in his absolute
rejection of the theory of descent. It is extremely kind of Professor Plate to
utter the warning that he gives on p. 172 : ' Orthodox philosophy and theology
will joyfully seize upon Fleischmann's book, and regard it as a sign that the
doctrine of creation is resuming its proper place.' Plate is confusing the
theory of permanence with the doctrine of the creation. If the former be
abandoned, the latter still remains indispensable, as alone accounting for the
origin of the first forms. As I showed at the end of the preceding chapter,
the doctrine of the creation is a necessary premiss to every reasonable theory
of evolution. Cf. also my answer to Plate in the Biolog. Zentralblatt, XXI,
1901, No. 22, pp. 689, &o.
810 MODEKN BIOLOGY
correspond with the natural relationships existing between
them.1
•• i The species Camponotus maculatus F. is particularly rich
in forms, and is found all over the world. It now contains
about fifty subspecies, and within these again over a hundred
varieties.
In the same way the systematic classification of Coleoptera,
especially in the genus Carabus, has been revised by Gangl-
bauer and Born. In one of Paul Born's recent works on
Carabus monilis,2 he distinguishes twenty-one subspecies
within the species, many having previously been regarded
as distinct species, and these twenty-one subspecies comprise
together over fifty varieties. This gives us some idea of the
enormous number of forms belonging to some of the species
of the genus ; but it proves nothing against the existence of
good species among animals and plants, and rather confirms
their existence, for otherwise there would be no distinction
between species and subspecies. No one, for instance, would
take it into his head to question the right of Myrmica rubra
L. and rubida Latr. among ants, of Carabus monilis F. and
intricatus L. among Carabidae, of Dinar da dentata Grav.
and clavigera Fauv. among Staphylinidae to be regarded as
distinct species.
In some genera of animals (e.g. Dinarda) there are only
a few species and numerous subspecies and varieties ; whilst
in others (e.g. Camponotus and Carabus) there are a great
many species and a correspondingly large number of sub-
species and varieties ; and finally in other genera (e.g.
Rhynchites, a kind of weevil) there are a good many genuine
species, no subspecies, and only a few, quite unimportant
varieties.3 It would therefore be injudicious and inaccurate
to deny with Plate the existence of sharply defined species.
An excellent remark is made by Fr. Dahl,4 who says : ' Students
occupied with departments of science in which sharply defined
1 Cf. on this subject Aus:. Forel, ' t)ber Polymorphismus und Variation bei
den Ameisen ' (Zoolog. Jahrbucher, Suppl. VII, 1904, pp. 571-186).
2 ' Carabus monilis F. und seine Formen ' (InseJctenborse, XXI, 1904, Nos.
6-10).
3 Cf. Wasmann, Der Trichterwickler, 1884, Appendix on the biology and
classification of the species of Rhynchites and their relations.
4 ' Die physiologischeJjZuchtwahl im weiteren Sinne ' (Biolog. Zentralblait,
1906, No. 1, pp. 3-5), p.*14.
PEEIODS OF FIXED FOEMS 311
species do not occur, are apt to believe that there are no
good species in existence ; and those, on the other hand,
who have to deal exclusively with good species, cannot under-
stand that there may be none in other groups of animals.
Every scientist, who aims at forming a just opinion on questions
connected with the theory of descent, ought to have experience
in both kinds of work.'
Is the fixity of the organic species, that prevails at the
present time, to lead us to conclude that species are
absolutely invariable, and that therefore no evolution can have
taken place in their case ? Such a conclusion would be
premature, for, granted that an evolution of species took
place in previous ages, the results of it might be exactly what
we see about us in the Alluvial epoch in which we live. An
intelligent day-fly, prevented by the shortness of its life from
knowing anything of the alternation of seasons, after seeing
the trees in blossom for an hour or two, might equally well
conclude that the world around it was in an unchanging
state of perpetual spring, and had been originally created
in this condition ; and yet the fly would certainly be
mistaken. Let us beware of coming to a conclusion of
this kind ! Palaeontology teaches plainly enough that, in
previous ages also, comparatively long periods of fixity
have alternated with shorter periods of transformation of
organic forms.1
If we are at the present moment living in a period
of comparative fixity 'i of organic forms, we may seek
in vain for actual " changes in the species around us ;
but that circumstance proves nothing against the theory of
descent.
However, even now we can observe facts which serve as
evidence, direct or indirect, in favour of an evolution of the
organic forms. Let us consider first the direct evidence,
although it must needs be very scanty.
1 Cf. K. von Zittel, Grundziigeder Palaontologie, p. 15; also 0. Heer, Urwald
der Schweiz, chapter 18. See also p. 287, note 1.
812 MODERN BIOLOGY
2. DIRECT EVIDENCE IN SUPPORT OF THE THEORY OF
EVOLUTION
It has recently been shown by Hugo de Vries l thai ;ii
the present time many plants are still in a period of evolu-
tion, i.e. they are producing new forms which are as sharply
denned, as independent, and as free from variations as real,
systematic species. According to de Vries, the evening prim-
rose (Ocnothera Lamarckiana) is now in a period of mutation.
There is no trace of any Darwinian natural selection as causing
or influencing this mutation ; the new varieties come into
being simply in consequence of the interior laws of evolution
in the form undergoing change, and not in any way through
the force of natural selection. This suggests the idea that
oven at the present time the process of race-evolution is not
complete in the case of all species. With regard to Darwin's
theory of natural selection de Vries says (' Die Mutations-
theorie,' II, p. 667) : ' Natural selection is a sieve ; it sifts out,
but produces nothing, although it is often 'wrongly asserted
to do so. The theory of selection ought not to take into
account the origin of what it eliminates.'
Many eminent zoologists and palaeontologists, such as
Waagen, Koken, Scott, Steinmann, Abel, &c.,3 have expressed
themselves in favour of the theory of mutation in the animal
kingdom. In fact, all the authors who accept an ' abrupt '
or * explosive ' or ' iterative ' development of forms in the
evolution of the race, such as Kolliker (1864), Emery
(1893), and Bateson (1894), are approximating to the view
1 Die Mutationstheorie : Versuche und Bcobachttingen ilber die Entstehung
n>n Artcn im Pfianzcnnichc, I, Leipzig, 1901 ; II, 1903. Cf. also Biolog.
Zentralblatt, XXI, 1901, Nos. 9 and 10 ; XXII, 1902, Nos. 16-19 ; XXIV,
1904, Nos. 5-7. ' Altere und neuere Selektionsmethoolcn ' (ibid. XXVI, 1900,
Nos. 13-15, pp. 385-395). J. Wiesbaur (Kulturproben a-its dem Schultjartcn
des StiftungsgymtMsiums Du-ppau, 1904, p. 42) assorts that within thirty years
he has twice observed the spontaneous growth of new plants. For a criticism
of the theory of mutation see also ,1. Keinke. Kinlcitinxj in die tJieorct incite
Biologic, pp. 518, &c. According to J. Beinke the range of mutation is extremely
limited.
3 For the bibliography of the subject see especially E. Koken, Paliiontologie
und Dfszcndcnzlchrc, Jena, 1902 ; also W. B. Scott, ' On variations and
mutations' (American Journal of Science, XLVIII, 1894, pp. 355-374); M.
Staudfuss. K.rpcrimcnteUe zoolixjinchc tftudicn mil Lepidopttrcn, Zurich, 1898;
J. Uross. ' Ober eim'ne Be/iehungen von Vererbung und Variation ' (Riolog.
Zftitmlbliitt, 1900, Nos. 13-18). dross rejects mutation as a factor in forming
species among animals. (See pp. 555, 501, &c.)
DIRECT EVIDENCE OF EVOLUTION 813
of the theory of mutation held by Korschinsky, de Vries, and
other botanists.
I should like to draw particular attention to the opinion
expressed by Zittel (* Grundziige der Palaontologie,' 1908,
pp. 14, 15) that periods of rapid and slow transformation
often alternate in the evolution of a race, for this opinion
probably is nearest to the truth.
Linnaeus stated that new forms could be produced
by crossing different species, and this is a very suggestive
idea as regards the theory of evolution. As far as the vegetable
kingdom is concerned, Kerner von Marilaun has proved in
his ' Pflanzenleben ' (II, 1898, pp. 565, &c.), that at the present
Li mo not only new varieties and subspecies, but new systematic
species, can be produced in this manner. Even J. Reinko,1
who has adopted a very critical attitude towards the evidence
in support of the theory of evolution, agrees with Kerner von
Marilaun on this point, and refers especially to the genera
Rubus, Salix, and Hicracium as instances of groups of forms
in which new typos are still being developed, that behave like
genuine species. There is, in fact, among plants a good deal
of direct evidence in favour of the theory of descent, although
this evidence may not be of a very important nature.
It is impossible to discuss in detail all the modern views
on the subject of evolution of species in the vegetable kingdom.
Most of these views coincide with Niigoli's ; they draw a sharp
distinction between organic characteristics and those due to
adaptation, and they refer the former to interior, and the latter
to exterior causes. I need allude here only to two works,
viz. Ed. Fischer's ' Die biologische Arten der parasitischen
Pilze und die Entstehung neuer Formen im Pflanzenreich '
(' Biological species of parasitic fungi and the origin of new
forms in the vegetable kingdom'),2 and C. Correns' 'Experi-
mentelle Untersuchungen fiber die Entstehung der Arten auf
botanischem Gebiet ' (* Experimental investigations regarding
the origin of species among plants').3 Correns' verdict upon
the theory of selection is interesting ; he says : ' Natural
1 Einleitung in die theoretische Biologic., 1901, pp. 542, &o.
3 Verhandl. der Schweiz. Naturforsch, Oesellsch. (Proceedings of the Associa-
tion of Swiss Naturalists), eighty-sixth annual meeting at Locarno, September
1903.
8 Archiv f\\r Rassen- und Oesellschaftebiologie, I, 1904, Part I, pp. 27-52.
314 MODEEN BIOLOGY
selection does nothing but weed out ; it has laid aside innumer-
able forms, and so has created gaps, but it has never produced
anything new.' This opinion agrees fully with my own
(Chapter IX, p. 260). In the animal world it is much more
difficult to study the problem of mutation by way of observation
and experiment than it is in the vegetable world.1 This may
seem strange at first sight, because most successful results
have been obtained by the artificial selection practised in
breeding the domestic animals. But these triumphs of
selection are completely worthless as affording any evidence
of the origin of new species, for all the varieties and breeds of
our domestic animals, produced by artificial selection main-
tained for hundreds or even thousands of years, are deficient
in the one quality oi fixity, which alone could give them
any positive value as aiding the solution of our problem.
There is not one artificial breed, no matter how well defined
or how far divergent from the primitive form, that can preserve
its characteristics without the help of man ; left to itself, it
invariably reverts in course of time to the original wild type.2
They supply, therefore, no evidence at all of the origin of new
species under natural conditions, because natural species
must necessarily be constant, whereas all artificially produced
breeds are liable to change. I do not mean to imply that the
interesting observations, made by Charles Darwin and his
1 I may incidentally remark that Schmankewitsch's famous attempts to
turn the crab Artemia salina into a Branchipus, by diminishing the amount
of salt in the water, can no longer be regarded as furnishing trustworthy evi-
dence. Cf. Ad. Steuer, ' Der gegenwartige Stand der Frage liber die Variationen
von Artemia salina Leach * (Verhandl. der k. k. Zool. Botan. Gesellsch., Vienna,
1903, pp. 145, &c.). The result of Steuer's investigations is given on p. 150:
' Just as under natural surroundings no Artemia can ever become a Branchipus,
or vice versa, so, most certainly, no one will ever succeed in transforming one
creature into the other by artificial means in an aquarium.' On the subject
of the alleged capacity for transformation of Artemia salina see M. Samter and
R. Heymons, ' Die Variationen von Artemia salina ' (Supplement to the
Verhandl. der Preuss. Alcademie der Wissenschaft, 1902); Cesare Artom, 'Note
critiche alle osservazioni del Loeb sulP Artemia salina ' (Biolog. ZentralbL
1906, No. 7, pp. 204-208). I do not propose to discuss the very interesting
experiments on the influence of heat on the colour of butterflies (Dorfmeister,
Weismann, Standfuss, Urech, Fischer, von Linden, &c.), and on that of
cochineal insects (Chr. Schroder), as the range of variation scarcely exceeds
that of ' Saisondimorphismus ' under natural circumstances. These experi-
ments, however, prove sufficiently that the direct action of exterior causes
is of great importance in the phylogeny of the forms in question.
2 A very good summary and criticism of facts and statements on this
subject is given by Yves Delage in his book, La structure du Protoplasma et
les theories sur Vheredite, 1895, pp. 295-298.
EVOLUTION OF DINAKDA 315
followers, on the methods and results of artificial selection
are without bearing upon the question of descent ; on the
contrary, they are of great value in this connexion, but they
tend to prove the exact opposite of what the followers of
Darwin desire. Instead of showing that new species " can
be formed on the lines of artificial selection, they have proved
that this never occurs. At the present time scientific men f
are becoming more and more convinced that facts do not
justify the comparison, set up by Darwin and his adherents,
between artificial selection and the processes whereby new
species are formed under natural circumstances. This com-
parison has found its scientific expression in the theory of
selection. If we want to find actual evidence of the evolution
of new species in phenomena of our own day, we must begin
by setting aside as useless all artificially produced breeds, and
we must limit our observation to the processes of natural
and independent formation of new varieties. But this is
easier said than done ! For where can we discover such
processes, seeing that we are living in a period when the
organic forms are fixed ?
3. THE EVOLUTION OF THE FOKMS OF DlNARDA
As proof that nevertheless such processes are still going on,
though they are not of frequent occurrence, and can be regarded
as satisfactory evidence only after very minute observation
of facts, I may refer to an instance that I discovered in the
course of my own research-work.
As a full account of it has already appeared in the Bio-
logisches Zentralblatt,1 I shall only refer shortly to the most
important points connected with it.
In the nests of ants living in northern and central Europe are
found various kinds of beetles of the genus Dinarda, Stapliylini-
dae of the sub-family Aleocharinae. In shape these beetles are
broad and flat in front and sharply pointed behind, and they
belong to the offensive type (Trutztypus) of ant-inquilines,
1 * Gibt es tatsachlich Arten, die heute noch in der Stammesentwicklung
begriffen sind ? Mit allgemeineren Bemerkungen iiber die Entwickhmg
der Myrmekophilie und Termitophilie und fiber das Wesen der Symphilie*
(Biolog. Zentralblatt, XXI, 1901, Nos. 22 and 23).
316
MODEEN BIOLOGY
FIG. 29. — Dinarda Maerkeli Ksw.
(original).
FIG. 30. — Dinarda dentata
Grav. (original).
FIG. 31. — Dinarda Hagensi
Wasm. (original).
FIG. 32. — Dinarda pygmaea
Wasm. (original).
The accompanying illustrations represent the four species of Dinarda that
occur in central Europe, and show their relative size and shape. In
colouring they resemble their hosts, viz. they are red and blackish. In D.
Maerkeli and D. dentata the wing-sheaths and the sides of the prothorax
are reddish brown; in D. Hagensi they are of a brighter red, and this
colour extends further, as far as the base of the antennae and of the
abdomen. In the smaller D. pygmaea the wing-sheaths are of a dark
reddish brown, with a black spot round the scutellum ; the sides of the
prothorax have a brownish tinge at their edge only. The rest of the
body is almost black, with the exception of the legs.
DINAEDA AND THEIE GUEST-ANTS 317
i.e. their structure renders them invulnerable to the attacks
of their hosts and enables them to defy them, so that tqe
ants tolerate their presence. There is no spot in the Dinarda's
body that the ants can reach with their jaws, if they wish to
attack them. The whole genus Dinarda belongs to this
offensive type, but the various species assume various forms
adapted to the peculiarities of their hosts, for each species
of Dinarda has its own especial host. D. dentata (fig. 30)
lives with the red ants (Formica sanguinea), D. Maerketi
(fig. 29) with the wood-ants (F. rufa), D. Hagensi (fig. 31)
with Formica exsecta, D. pygmaea (fig. 32) with F. rufibarbis,
and especially with a small, dark-coloured subspecies known
as F. fusco-rufibarbis. A series of observations and experiments,
carried on for many years, enabled me to establish the fact that
the differences existing between these four species of Dinarda
might be very simply referred to the following principle : —
The larger species of Dinarda always lives with the larger
species of Formica and with such as build large ant-hills ; the
smaller species of Dinarda lives with the smaller species of
Formica, and with such as occupy simple nests in the earth.
F. rufa and exsecta build ant-hills, and rufa is considerably
bigger than exsecta ; therefore the biggest and broadest species
of Dinarda, D. Maerkeli, lives with F. rufa ; the smaller
D. Hagensi with F. exsecta. The latter Dinarda is almost
as large as D. dentata, which lives with F. sanguinea, although
this ant is considerably bigger than F. exsecta, but sanguinea
generally constructs simple nests in the earth, which have
at best a little heap of vegetable matter at the top, whereas
F. exsecta builds real ant-hills. F. fusco-rufibarbis is the
smallest and darkest of all the above-mentioned kinds of
ants, and it always makes simple nests in the earth ; therefore
D. pygmaea, that lives with it, is the smallest and darkest of
all the Dinarda family.
As the Dinarda are inquilines of the offensive type, and
are tolerated with indifference because of their normal invulner-
ability, it follows that only smaller Dinarda can live among
small ants than among large ants, for the larger the Dinarda
in proportion to its hosts, the more easily can they seize it
by its antennae or legs, hold it fast, kill and devour it. I
have established this fact by actual experiments. In the same
318 MODEKN BIOLOGY
way among ants living in simple nests in the earth only a
smaller Dinar da can make its way, than among those ants
in whose spacious ant-hills there must be many convenient
hiding-places for the beetles. But why does the darkest
Dinarda live with the darkest ants ? For the same reason.
Because the Dinarda are the largest inquilines of the offensive
type, and therefore attract the ants' attention in an especial
degree, there must be a certain amount of similarity in colouring
between them and their normal hosts, in order that they may
more easily escape notice. Now all the above-mentioned
species of ants are of two colours, red and black, and so all the
four corresponding species of Dinarda wear the same livery,
and F. fusco-rufibarbis, being the ant darkest in colour and
most nearly approaching uniformity in tint, is the host of
Dinarda pygmaea, which is the darkest beetle, and the one
most nearly approaching uniformity in tint.
For the facts just stated I can offer no explanation but the
following, that our four species of Dinarda are four different
forms of one and the same generic type, and their differences
are due to adaptation to the four kinds of guest-ants. If we
assume that within the genus Dinarda an evolution has taken
place, we must acknowledge that this evolution was determined
by the characteristics of the guest-ants, and took place in the
way described above. The result of a race-evolution of
Dinarda could be no other than that which we can observe
at the present day.
But has such a race-evolution really occurred ? Yes, for
there is important evidence to show that this evolution is not
yet ended, but is still going on before our eyes.
The following facts bear out the above statement. In the
the first place, there are certain regions in central Europe
in which the four forms of Dinarda live side by side, after
the fashion of genuine systematic species, having their points
of difference fixed. Each inhabits the nests of the ants to
which it corresponds. Secondly, there are other districts in
northern and central Europe, in which only two forms of
Dinarda (dentata and Maerkeli) occur, living with their respec-
tive ants (F. sanguinea and rufa), whilst F. exsecta and fusco-
rufibarbis have no Dinarda as guests in those regions. Thirdly,
there are other regions in central Europe occupying a position
DINAEDA AND^THEIE GUEST-ANTS 319
between these two extremes, inasmuch as F. sanguinea and
rufa possess their proper kinds of. Dinarda (dentata and Maerkeli),
whilst F. exsecta entertains a transitional form midway between
dentata and Hagensi, and among F. fusco-rufibarbis occur forms
connecting dentata and pygmaea. This can be observed best
in the case of the Dinarda that is the guest of F. fusco-rufibarbis.
The very small, dark D. pygmaea, which is completely adapted
to this ant, is connected by a series of transitional forms,
having a different geographical distribution, with D. dentata,
that lives with F. sanguinea.
In many parts of central and northern Europe no special
kind of Dinarda is found living with F. rufibarbis, but in other
places there is a kind that scarcely differs from D. dentata.
In other districts again there is the D. dentata var. minor,
which is already distinguished as a variety of dentata, and
in others the D. pygmaea var. dentatoides, which closely
approximates to the typical pygmaea ; finally, in other districts
the genuine D. pygmaea is found, either alone, or as well as
the var. dentatoides. In order to understand this geographical
distribution, we must not lose sight of the fact that, in each
district, Dinarda occurs among F. rufibarbis with greater
regularity and frequency the more widely the Dinarda form
corresponding to the ants in that locality diverges from the
dentata type, and the more closely it approximates to the
pygmaea type.
As a science, natural science cannot avoid seeking the
fixed pole about which phenomena revolve ; it must needs try
to discover the laws underlying the multiplicity of phenomena.
The law contained in the foregoing account of the distribution
of Dinarda may be stated as follows : — The specific evolution
of the forms of Dinarda has reached different stages in different
parts of geographical distribution. The adaptation of D.
dentata to F. sanguinea and of D. Maerkeli to F. rufa is complete
all over northern and central Europe, but that of D. Hagensi
to F. exsecta and of D. pygmaea to F. fusco-rufibarbis is still
incomplete ; in fact, the last-named adaptation is in progress,
being complete in some localities, having advanced half-way
in others, and in some places having scarcely begun or even
not begun at all. Kecent discoveries show that the adaptation
of Dinarda Hagensi to Formica exsecta has advanced further
320 MODEEN BIOLOGY
in England and in the Siebengebirge on the Ehine than in other
parts of central Europe.
If we wish to determine more exactly the topographical
localities corresponding to the different stages of evolution in
Dinarda, we must distinguish general and particular local
influences. As a rule, the four forms of Dinarda seem to be
most sharply marked off from one another in those districts
of central Europe which first became free of ice and water
at the close of the last glacial period of the Pleistocene epoch,
such as the Khine valley above the Siebengebirge, southern
England, Bohemia, Silesia, &c. The fact that only two
species of Dinarda appear to occur in the central Alps and in
northern Europe agrees with this view. On the other hand
special local circumstances may contribute sometimes to a
quicker and sharper marking off of the species of Dinarda
living with F. rufibarbis. So, for instance, on the glacis of the
old fortress of Luxemburg, oil a plateau with steep edges,
where there are many nests of F. rufibarbis, but none of F.
sanguinea, I have found D. pygmaea var. dentatoides in the
rufibarbis nests, many specimens approximating very closely
to the typical pygmaea. I observed the same thing on the
steep hills of Pulvermuhl near Luxemburg, where similar
local conditions favour the development of Dinarda pygmaea.
But on the long ridges of hills between Luxemburg and Treves,
I found several Dinarda scarcely differing from the typical
dentata, in nests of F. rufibarbis at Ober-Anven ; the evolution
of a special Dinarda form among F. rufibarbis in this district
has probably been hindered, because the Dinarda, in passing
from one ants' nest to another, have had opportunities of
crossing with D. dentata living in the neighbouring nests of
F. sanguinea. If the rufibarbis nests are circumscribed by
the configuration of the locality, the evolution of a particular
form of Dinarda is doubtless facilitated, although it does not
appear to be absolutely necessary that the nests should be
isolated ; for at Exaten in Dutch Limburg for many years
I used to find in a nest of F. rufibarbis var. fusco-rufibarbis
specimens only of D. dentata var. minor, with no transitional
forms to the typical D. dentata, although only about thirty
yards away, on the same flat stretch of ground, there were
several nests of F. sanguinea, inhabited by the typical D. dentata.
SPECIES OF DINAEDA 321
The objection may be raised that these phenomena are
arguments for an evolution within the species only, and not
for an evolution of new species from others. In this case
what is meant by a ' species ' ? Is it a natural or a systematic
species ? l
That our four parti-coloured forms of Dinarda belong
to one natural species is a matter of course, as soon as
they can be proved to be of common origin. But if we ask
whether they ought to be reckoned as belonging to one sys-
tematic species, the answer is not so" simple. In case they
are all declared to be only systematic subspecies of D. dentata
— an opinion that I put forward as long ago as 1896 2 — they
are nevertheless subspecies constituting different stages on
the way to the formation of genuine species. D. dentata, which
stands nearest to the hypothetical primitive form, and
D. Maerkeli, which was the earliest to branch off from it,
are already quite as sharply differentiated from one another
as are many other systematic species. D. Hagensi and pygmaea
are at a less advanced stage of evolution, and have been
differentiated as independent forms only in some of the
localities occupied by the ants that are their hosts. It is,
however, quite immaterial to the question under discussion,
whether we declare the four parti-coloured forms of Dinarda
occurring among the Fauna of northern and central Europe
to be real systematic species, or only races or subspecies at
different stages on the way to forming species, for in neither
case is it possible to avoid the assumption that we have here
a real instance of evolution, the aim of which is the production
of forms adapted to a particular way of life, and destined
finally to split up into distinct species.
The process of evolution extends even to the generic
characteristics of Dinarda. In Dinarda Hagensi of the
Siebengebirge (von Hagens) and southern England (Donis-
thorpe), the- edge of the wing-sheaths is not convex and
carinated, as it should be, according to the systematic descrip-
tion of the genus Dinarda and of all the genera of Dinardini,
1 For the distinction between these two ideas see pp. 296, &c., in the pre-
ceding chapter.
2 * Dinarda- Arten oder Rassen ? ' (Vienna, Entoniolog. Zeitung, XV,
Parts 4 and 5, pp. 125-142).
y
322 MODEKN BIOLOGY
but it is simply curved, as it is in the other cognate Aleocharinae.1
In other specimens of Hagensi, from Linz on the Khine, the
edge of the wing-sheaths is convex and carinated, as it is in
D. dentata. There are also forms of Hagensi, standing midway
between the two to which I have referred, with respect to
the formation of the edge of their wing-sheaths. This shows
plainly that the generic characteristics also of Dinarda have
only a relative value, and that they are affected by the same
laws of natural evolution as those that differentiate species
and subspecies within the genus. I shall be able later on to
establish this conclusion more firmly by means of a comparison
with the D. nigrita of southern Europe. How can any one
seriously maintain that the phenomena which I have observed
in the evolution of Dinarda serve only as arguments in support
of an evolution within the systematic species ?
Some one may, perhaps, grant that within the genus
Dinarda such a process of evolution is actually still going on,
but he may say that he does not see what it has to do with
our acceptance of the theory of evolution in general, as possibly
this is merely an exceptional case. It is quite true that we
have here an exception to the usual fixity of systematic species,
and it would be a great mistake to assert that all, or even
most, genera of animals are still forming new species in the
same way as the Dinarda. It would, however, be equally
wrong to deny that these phenomena have any weight as
evidence in support of the theory of evolution, because excep-
tions must not be taken as a rule. If it is once granted that
the four parti-coloured species of Dinarda are really con-
nected by having a common origin, we cannot avoid comparing
them with the black D. nigrita of southern Europe, which
lives with a black Myrmicide ant near the Mediterranean
(Apliaenogaster testaceopilosa) . This species differs so widely
from its northern relatives, that Casey has recently decided,
with much reason for so doing, that it ought to be regarded
as a distinct genus Chitosa, and yet it is undoubtedly related
to the genuine Dinarda, for, when we possess more information
as to its mode of life, we shall probably find that the most
1 Cf. Wasmann, ' Beispiele rezenter Artenbildung bei Ameisengasten
und Termitengasten ' (written in honour of Rosenthal, Biolog. Zentralblatt,
Nos. 17 and 18, pp. 565-580). See especially p. 566.
SPECIES OF DINAEDA 323
important morphological characteristics distinguishing D.
nigrita are due to adaptation, just as we have already found
them to be in the case of our parti-coloured species of Dinarda.
That the differences in the former instances are much greater
than in the latter can easily be accounted for, inasmuch as
D. nigrita lives with an ant that is not only generically different
from Formica, but belongs to another subfamily, whereas our
northern Dinarda all live with species of one and the same
genus Formica. Moreover, D. nigrita resembles its northern
relatives in those systematic characteristics which are inde-
pendent of the offensive type (Trutztypus), especially in the
formation of the parts of the mouth and in the peculiarly
shaped tongue. We must therefore assume that it is descended
from the same primitive form as our Dinarda, and has acquired
its present form by a process analogous to that which has
produced the northern Dinarda, viz. by adaptation to the
ants that are its hosts.
It would plainly be inconsistent to admit that the dif-
ferentiation of our parti- coloured Dinarda was the result of a
real process of evolution, and to deny that in all probability
an identical process of evolution has led to the differentiation
of the genera Dinarda and Chitosa. This comparison certainly
proves that in certain cases the principle of evolution may, and
even must, be applied to systematic genera of the same family.
A few remarks must be made in order to avoid misunder-
standings, to which my account of the evolution of Dinarda
might possibly give rise.
In all that is essential, the same factors of adaptation,
which caused, and are still causing, the parti-coloured Dinarda
to be differentiated from one another, led to the differentiation
of the genera Dinarda and Chitosa from one common primitive
form, but in the latter case the evolution was less slow and
gradual than in the former. The great difference existing
between the two genera of guest-ants, Formica and Aphaeno-
gaster, must have brought about a more rapid differentiation of
the Dinardini that were adapting themselves to them. We
shall the more readily accept this statement if we remember
that in the Pleistocene epoch, in which this hypothetical process
of evolution must have taken place, there was probably a
rapid succession of climatic changes, which would facilitate a
Y 2
824 MODEKN BIOLOGY
rapid alteration in the area of distribution of the various
kinds of ants.
Let us assume that, in consequence of some climatic
change, the southern genus Aphaenog aster extended its area
of distribution towards the north, encroaching on a locality
hitherto occupied by Formica, which gradually died out in
that neighbourhood, so that the border line of its zone of
distribution was drawn further north. A Dinarda-like
beetle, transferring its quarters from the nests of the Formica,
that was becoming extinct, to those of the Aphaenogaster,
that was becoming more common, would be forced to adapt
itself to its new hosts, if it were not to be exterminated by them.
This circumstance would give a great impetus to the speedy
formation of new varieties, or to mutations per saltum in a
direction favourable to this adaptation ; in fact, the tendency
to evolution would receive a fresh impulse. We cannot
account for all this, unless we assume the existence of interior
laws of evolution,1 which react beneficially in response to
exterior influences ; these laws are indispensable, if we
have to recognise the occurrence of advantageous adaptation.
We cannot indeed explain how each exterior circumstance
acts upon the interior capacity for adaptation in the organism,
but we are equally unable to explain how, under the stimulus
of light, animal protoplasm is made capable of reacting by
forming specks of pigment susceptible to light. The great
secret of life is hidden in the capacity for adaptation possessed
by living organisms, and we must acknowledge that this
secret exists, and not fall into the error of Darwinism, and
deny its existence because it is ' mechanically inexplicable.' 3
If we do not admit this, there is no alternative but to
regard the first formation of beneficial modifications as purely
accidental ; a theory of chance can never be the foundation of
a theory of evolution.
1 That this assumption is by no means devoid of a material basis has
already been shown. See Chapter VI, pp. 177, &c. and Chapter IX, p. 297.
2 It is a matter for regret that August Weismann, who is otherwise so
keen-sighted, in his Lectures on the Evolution Theory still brands the assump-
tion of a capacity for adaptation on the part of organisms as ' mystical '
or * extraordinary,' although in discussing what he regards as the smallest
units of life (biophors and determinants) he speaks of * vital affinities,' which
is only another name for design inherent in the organism. Cf. I, p. 374 and
II, p. 36 (Eng. trana.) ; see also p. 176 of this work.
EVOLUTION OF DINAEDA ' 325
We may, therefore, assume that the process of differentiat-
ing the genera Dinarda and Chitosa from one common primitive
form could not have been as gradual as the subsequent process
of differentiating the genuine parti-coloured Dinarda from one
another. The former probably took place per saltum, after
the fashion of de Vries' mutation theory.
This assumption seems all the more necessary in order
to account for the first production of the offensive type
(Trutztypus) from the primitive form of the Dinar dini, for
their nearest relatives of the genus Thiasophila differ from
them so widely that it would have taken hundreds of thousands
of years to bridge the gulf between them, if their evolution
had been of the gradual sort, such as Darwin imagined. As
a matter of fact, however, the primitive form of the Dinardini
must have come into being in a comparatively short time, at
the end of the Tertiary period, or at the beginning of the
Pleistocene. This can be proved with a fair amount of certainty
from the geographical distribution of Dinarda. The genus
Thiasophila occurs in North America as an inquiline among
Formica, but the genus Dinarda is not found there, although
the species of Formica are as widely distributed and of as
frequent occurrence in North America as they are with us ;
in fact, they have attained to a more manifold evolution.
It follows that the primitive' form of Dinarda can have been
produced only after North America had been completely
cut off from Europe and northern Asia by the ocean,
which certainly did not take place before the close of the
Tertiary period. Otherwise it is inexplicable why the
genus Dinarda is limited to the northern half of the old
world, and does not occur in North America, in spite of
the abundance of species of Formica, which are mostly identical
with our own.
What does this instance of evolution on the part of Dinarda
really show ? That there are cases in which the hypothesis
of the theory of evolution assumes a more tangible form and
appears more irrefutable, the more closely we examine the
details of the facts presented to us. But if we try to trace back
the more remote phylogeny of the Dinardini, we are involved
in obscurity.
The same remark applies to other problems connected with
326 MODEKN BIOLOGY
the theory of descent. As long as they refer to groups of
forms within narrow limits, they appear trustworthy, if
they are true at all ; but when their application is extended
to general relationships between higher orders, classes or groups
of animals, they are apt to become vague and uncertain, and
their charm is often one that attracts only from a distance,
as Fleischmann says, in his work on the Theory of Descent
(' Die Deszendenztheorie ').1 We may therefore accept the
doctrine of evolution without demur, — in so far as it has a
scientific basis, and applies to definite groups of forms with
a sufficient degree of probability ; but, in accepting it, we
may decidedly reject, as having no scientific support, those
* Postulates ' proposed to us by monism in its name.
And what does this instance of evolution not show ? That
ant-inquilines of other biological types have evolved in the
same way and through the same causes as the Dinardini
belonging to the offensive type (Trutztypus) ; for precisely
because other inquilines do not belong to this type, they are
subject to other laws of adaptation, which we shall presently
have to consider. No one would be justified in concluding,
from what has been said of the Dinar da forms, that all species
of animals must have been produced in a similar fashion
and for the same reasons. If such a conclusion were un-
justifiable on no other grounds, it would be quite untenable
for the reason that the great majority of the systematic differ-
ences between species of the same genus are biologically
indifferent, and are neither serviceable nor injurious to their
owner ; therefore they afford no points d'appui for the ' selec-
tion of the fittest.' The interior laws of evolution in living
organisms, which form the indispensable basis underlying
the evolution also of Dinar da, have a much greater and more
general significance in other departments of the doctrine
of evolution than they have here, although it is by no means
so devoid of all limitations, as Eimer and other supporters
of orthogenesis assume to be the case.
1 See also Stimmen aus Maria-Loach, LXTI, pp. 116, &c. : 'Eine Reaktion
gegen die Deszendenztheorie.'
INDIRECT EVIDENCE OP EVOLUTION 327
4. INDIRECT EVIDENCE IN SUPPORT OF THE THEORY
OF EVOLUTION
Let us now turn to the indirect evidence supporting the
theory of descent. In comparison with the direct evidence
it is wonderfully abundant and varied, and may be derived
from every department of biological research, especially
from comparative morphology and comparative morphogeny,1
from comparative biology, and especially from palaeontology,
which seeks to establish the relationship between the animals
and plants of the present day and the fossils of previous ages.
In Chapter IX (pp. 274, &c.) enough has been said to prove
the importance of palaeontological facts in establishing the
occurrence of an evolution of species. As it is not my purpose
to write a textbook of the theory of descent, I will only add
a few pieces of circumstantial evidence in support of it, taken
from my special department of study, viz. from the com-
parative morphology and biology of inquilines among ants
and termites.3
1 Particular attention should be paid to the phenomena of parasitic degene-
ration among animals, for it frequently results in a complete transformation
or rather degeneration of the adult animal, so that the place in a natural
system, and consequently the connexion of these forms with others derived
from the same stock, can be traced only through the larvae, or at a very early
stage of development. Instances of this occur among the parasitic Copepods
(in the families of Lernaeopoda and Lernaeae), and the parasitic Cirripeds
(in the suborder of Rhizocephala). As a rule, degeneration characterises
parasitic adaptation, and specific transformation prevails in the symbiotic
adaptation of the inquilines of ants and termites to their hosts.
a Fuller details may be found in the third and fourth parts of the work :
' Gibt es tatsachlich Arten ? ' &c. (Biolog. ZentraMatt, 1901, Nos. 21 and 22) ;
also in ' Neue Dorylinengaste aus dem neotropischen und athiopischen Faunen-
gebiet' (Zoologische Jahrbucher, Abteilung fur Systematik, XIV, 1900, Part 3,
pp. 215-289, 275, &c.); ' Termiten, Termitophilen und Myrmekophilen gesam-
melt auf Ceylon von Dr. W. Horn, mit anderem ostindischen Material bearbeitet '
(Zoologische Jahrbucher, Abteilung fur Systematik, XVII, 1902, Part I, pp.
99-164, plates 4 and 5) ; ' Biologische und phylogenetische Bcmerkungen
iiber die Dorylinengaste der Alten und der Neuen Welt, mit besonderer Beriick-
sichtigung ihrer Konvergenzerscheinungen ' ( Verhandl. der Deutschen Zoolog,
Gesellschaft, 1902, pp. 86-98) ; ' Neue Bestatigungen der Lomechusa-Pseudo-
gynen-Theorie ' (ibid. pp. 98-108) ; ' Zum Mimikrytypus der Dorylinengaste '
(Zoolog. Anzeiger, 1903, No. 704, pp. 581-590); '*Zur naheren Kenntnis des
echten Gastverhaltnisses bei den Ameisen und Termitengasten ' (Biolog.
ZentraMatt, 1903, Nos. 2, 5, 6, 7, 8) ; ' Ein neuer Atemeles aus Luxemburg '
(Deutsche Entomolog. Zeitschrift, 1904, Part T, pp. 9-11) ; ' Zur Kenntnis der
Gaste der Treiberameisen am oberen Kongo ' (Zoolog. Jahrbucher, Supplement
VII, 1904, pp. 611-682 with plates 31-33) ; ' Zur Lebensweise von Atemeles pra-
tensoides ' (Zeitschr. fur wissensch. Insektenbiologie, II, 1906, Parts 1 and 2) ;
328 MODEKN BIOLOGY
One thing to be learnt from these phenomena is that it is
absolutely necessary to accept the fact of an evolution of
the systematic species, and often of the genera and even of the
families, within these orders of insects to which most of the
inquilines among ants and termites belong. They warn us
also to be on our guard against over-hasty generalisations,
such as are being made recklessly with regard to the theory
of descent. In many cases the occurrence of a real evolution
of some particular forms is so strongly borne out by facts,
that no thoughtful student of natural science can refuse to
accept it, but in other cases there are serious difficulties in
the way of accounting for phenomena by means of evolution.
It is altogether impossible to apply universally any hard
and fast method, like those which some advocates of the
theory of descent have adopted and employ as talismans to
explain everything.
This is no less true of Weismann's view of the all-importance
of natural selection, than it is of Eimer's diametrically opposed
theory of orthogenesis. Facts are obstinate things, and
refuse to fit in with these theories — what suits one, does not
agree with another. The evolution of those inquilines among
ants and termites which, like Dinarda, belong to the offensive
type (Trutztypus) cannot be the result of the same factors as
have produced the inquilines of the mimetic type ; and these
again must owe their peculiarities to a different principle
of evolution from the genuine inquilines of the symphilic
type.
Nature is intolerant of constraint applied in favour of any
particular theory ; any one who tries to account for all
phenomena in the same way is doomed to failure. Eimer's
orthogenesis, according to which interior laws of growth
with a definite tendency are the sole causes of evolution,
breaks down when applied to inquilines of the offensive and
mimetic types, just as Weismann's natural selection theory
does when applied to inquilines of the symphilic type.1
Beispiele rezenter Arteribildung bei Ameisengasten und Termitengdsten (see
p. 322, note 1). Works dealing with Termitoxenia will be mentioned in §10
of this chapter.
1 Cf. the remarks on race-evolution and its causes in Chapter IX, pp. 294,
etc. With regard to botany, von Wettstein especially has expressed himself in
very similar terms, and has shown ' that it is impossible to refer all the pheno-
INDIRECT EVIDENCE OF EVOLUTION 329
The following general considerations are important by
way of introduction to a more detailed comparison of the
theories of permanence and descent, with reference to the
comparative morphology and biology of ant and termite
inquilines.
By far the greater number of regular inquilines among
ants and termites, that show any marked degree of adaptation
to the life of their hosts, belong to the order of beetles. This
order is geologically older than either ants or termites, for a
number of beetles belong to the Triassic strata, i.e. to the oldest
period of the Mesozoic age.
Moreover, this order of insects had attained so high a
development by the middle of the Mesozoic age, that in the
Black Jurassic are found representatives of almost all our
present families and genera of beetles. It was not until the
Caenozoic age that ants and termites reached a corresponding
height of development. In the Tertiary period they began to
form regularly organised states and to play an important
part in nature. Before that time, therefore, other insects
had no reason for adapting themselves to become inquilines
among ants or termites ; the conditions that could motive
such adaptation were wanting. We must, then, adopt one
of two hypotheses : — In the Tertiary period there was a direct
creation of a number of new families of beetles, which are ex-
clusively myrmecophile or termitophile, such as the Paussidae,
Clavigeridae, Gnostidae, Ectrephidae, Bhysopaussidae, &c.,
and of still more numerous myrmecophile or termitophile
genera in other families of beetles, among the Staphylinidae,
Scarabaeidae, &c. — and that such a creation took place is
from the palaeontological point of view most improbable —
or else the families and genera of ant and termite inquilines
have been evolved from primitive forms,1 which lived in the
Mesozoic age, and only at a later date adopted the myrme-
cophile or termitophile mode of life.
mena observed in the production of new forms in the vegetable kingdom to
the same causes ' (Berichte der deutschen Botan. Gesellschaft, XVIIT, 1900,
p. 200). Von Wettstein lays great stress on the distinction between char-
acteristics due to organisation and those due to adaptation, but within the
latter group we are forced to distinguish a number of different causes.
1 These primitive forms belonged to other systematic families and genera
of already existing beetles.
330 MODERN BIOLOGY
The latter hypothesis seems far more probable than the
former, not merely for scientific, but for philosophical reasons,
as, if we can account for the origin of myrmecophile and
termitophile forms by showing them to be natural phenomena
according with the theory of evolution, we ought not to have
recourse to any hypothesis involving direct new creations.
In order to enable my readers to form some idea of the
kind of evidence which a study of ant and termite inquilines
affords in support of the theory of descent, I will give a short
account of some of these creatures.
5. HYPOTHETICAL PHYLOGENY OF THE .LOMECHUSA
GROUP
Among the palsearctic and nearctic Fauna, i.e. in the
continent of Europe and in northern and central Asia on
the one hand, and in North America on the other, is a natural
group of closely related genera of Aleocharinae, which I have
classed together as the Lomechusa group, or Lomechusini.
They are the most highly developed genuine ant-inquilines
of the symphilic type among all the StapJiylinidae of the
northern hemisphere. In Europe and in Asia as far as the
tablelands of Tibet they are represented by the genera Lome-
chusa and Atemeles. The former lives exclusively with
definite species of ants, for instance Lomechusa strumosa
(fig. 33) is found only in the nests of Formica sanguined, and
the ants bring up the Lomechusa larvae (fig. 34).
Atemeles, on the contrary, lives with both Formica and
Myrmica ; they pass the greater part of their existence as
beetles with Myrmica rubra, but the larvae are brought up
by various species of Formica. Throughout North America
the Lomechusini are represented by the genus Xenodusa, and
the species found furthest south (Xenodusa Sharpi Wasm.)
occurs in Mexico. Xenodusa lives partly with Formica,
partly with Camponotus, so that it has two sets of hosts, like
our Atemeles ; the larvae are probably brought up by Formica.1
1 This supposition has been already confirmed in the case of Xenodusa
cava Lee. by P. Muckermann's observations in the Prairie du Chien, Wisconsin.
This Xenodusa causes its larvae to be brought up by a North American sub-
species of our red robber-ants (Formica sanguinea subsp. rubicunda Em.),
and, as in Europe, the breeding of these adopted larvae leads to the develop-
LOMECHUSINI 331
The extraordinarily long antennae and legs of Xenodusa
show a pronounced adaptation on the part of this genus to
their mode of life in the Camponotus nests. If these extremities
were not so long, it would be impossible for the beetles to
maintain their friendly intercourse with Camponotus, as the
ants are much larger than the Xenodusa, which are obliged
to raise themselves high on their long legs and to stretch up
their antennae, whenever they invite one of their huge hosts
to feed, and whenever they are fed in their turn.
A very interesting phylogenetic question here arises. With
which of the three genera of ants did the primitive form of
Lomechusa live, with Formica, Myrmica, or Camponotus ?
FIG. 33. — Lomechusa strumosa F. FIG. 34. — Larva of Lomechusa
(5 times the natural size). strumosa (5 times the
natural size).
Which of these genera can claim the honour of having trained
these genuine inquilines and of having, by breeding, developed
their capacity for adaptation and brought it to the highest
perfection by amical selection ? Camponotus is a cosmo-
politan genus of ants, and is represented by an immense
number of species in the southern hemisphere ; in fact, in the
south the species are more numerous and more varied than
in the north. The genus Myrmica belongs chiefly to the
palaearctic and nearctic region, but some few species are
found in Asia south of the Himalayas, especially in Burma,
and one species (Myrmica aberrans For.) in Australia. The
genus Formica is exclusively palaearctic and nearctic. Now
the geographical area of distribution of the Lomechusini
ment of pseudogynes in the ant colonies. The beetles are found, as a rule,
among Camponotus pennsylvanicus Deg. and pictus For. (Cf. Neue Bestati-
gungen der Lomechusa- Pseudogynen-Theorie, p. 106.)
332 MODEKN BIOLOGY
coincides with that of Formica, whilst those of Myrmica and
Camponotus are far more extensive. We may, therefore,
conclude with great probability that the Lomechusini are a
product of the symphilic instinct in the genus Formica, and
that the adaptation of Atemeles to Myrmica and of Xenodusa to
Camponotus was of later and secondary origin.
This is of course only hypothesis, but it is founded on facts,
and is very serviceable as enabling us to understand the
morphological and biological peculiarities of Lomechusini,
as well as their geographical distribution ; and without this
hypothesis it would be impossible to account for their actual
distribution. The remarkable fact that all the species of
Atemeles still cause Formica to bring up their larvae, although
at least the smaller of these species (At. emarginatus and
paradoxus) in other respects are better adapted to intercourse
with Myrmica, suggests the idea that their ancestors continued
as beetles to live with Formica and not with Myrmica. More-
over, a close examination of the morphological peculiarities
of the Lomechusini, from the biological point of view, would
show that fundamentally they are better adapted for intercourse
with the genus Formica. Therefore the genus Lomechusa,
which has remained faithful to its original kind of hosts, viz.
Formica, represents the highest stage of evolution of the
symphilic type among the Lomechusini.
The theory of permanence is incapable of giving an explana-
tion of any of these phenomena. It can only declare that the
various genera and species of the Lomechusini were created
for their normal hosts. It cannot suggest a reason why
the genera Atemeles and Xenodusa have more than one kind of
host, nor can it account for the high development of the tufts
of yellow hair and the other characteristics of the Lomechusini
that are connected with their adaptation to their hosts. Still
less can it tell us why the genus Camponotus in the southern
hemisphere does not enjoy the company of the beautiful
Xenodusa, whose long antennae and legs are, as it were, created
on purpose to fit it for friendly intercourse with Camponotus.
This is the harder to explain as the larvae of Camponotus, like
those of Formica, spin a cocoon before pupation. The only
ants able to render the Lomechusini larvae the attention that
they require, are those which are in the habit of covering
LOMECHUSINI 333
their own larvae with a case made of earth before they enter
on the pupal stage. We may therefore safely assert that
Atemeles are bound to have their larvae brought up by Formica,
because their other hosts of the genus Myrmica have pupae
without cocoons, and so cannot help the Atemeles larvae in
their preparations for pupation. But this is not a valid reason
in the case of Camponotus. If species of Xenodusa and of
Atemeles occur, nevertheless, within the area of distribution of
the genus Formica, it can be explained only on the hypothesis
that originally all the Lomechusini lived exclusively with
Formica, and afterwards spread to some extent to other genera
of ants (Myrmica and Camponotus), amongst which they
now spend the greater part of their imago existence.
Each change of host was accompanied by a further morpho-
logical differentiation of the three genera, Lomechusa, Atemeles,
and Xenodusa. Those species of Lomechusini which remained
faithful to one kind of hosts developed into genuine Lomechusa,
and continued to pass their whole existence in the company of
definite species of Formica ; whilst those species which accepted
the hospitality of two kinds of hosts developed into Atemeles
and Xenodusa, the former being adapted to associate with
Myrmica and the latter with Camponotus, although they
returned at times of propagation to the species of Formica
that could bring up their larvae. This phylogenetic theory
gives us the only natural explanation both of the common
morphological and biological characteristics of the Lomechusini,
and also of the differences that we find occurring within this
group of beetles.
As an example of evolution of differences between species
within the three genera of Lomechusini, let us consider more
particularly the species Atemeles. All the Atemeles have, as has
been stated, two kinds of hosts ; they pass the chief part of
their existence as beetles with Myrmica rubra, and in April
or May, when they lay their eggs, they migrate to the nests of
definite species of Formica, with whom they leave their young
to be brought up. The newly developed beetles return to the
Myrmica at midsummer or in the autumn. This migratory
life of Atemeles is biologically very interesting, and I have
therefore kept a record of hundreds of observations made upon
it, having studied the creature, partly under normal conditions,
334 MODEKN BIOLOGY
and partly as it lived in nests kept for the purpose of research.
I cannot do more here than give a brief resume of the results
of my investigations, so far as they bear upon the theory of
evolution.
Atemeles lives for one year, and spends the greater part
of its life with Myrmica, and the smaller part with Formica,
so that the former may be called the primary, and the latter
the secondary host of Atemeles. Phylogenetically, however,
the relation is reversed, because the adaptation of the Lome-
chusini to Formica is of earlier date than the adaptation of one
genus of this group, viz. Atemeles, to Myrmica. It is to this
adaptation that the species of Atemeles owe their common
generic characteristics, which distinguish them from Lomechusa.
On the other hand, the differences that mark off the individual
forms of Atemeles as distinct species are due to the differences in
the species of Formica, amongst which to this day the larvae
of Atemeles are brought up. In the nests of the various sub-
species of Myrmica rubra, i.e. among Myrmica scabrinodis,
laevinodis, ruginodis, rugulosa, sulcinodis, &c., it is not at all
uncommon to find several species of Atemeles at once ; but
in the colonies of Formica one definite form of Atemeles
invariably occurs, Atemeles emarginatus with Formica fusca,
Atemeles paradoxus with Formica rufibarbis, Atemeles pubicollis
with Formica rufa, the Foreli variety of Atemeles pubicollis
with Formica sanguinea, and Atemeles pratensoides with
Formica pratensis.
A comparison of Atemeles pubicollis with its relatives
shows most beautifully that the systematic differences dis-
tinguishing the various species of Atemeles from one another
are really due to adaptation to the particular species of Formica
with which Atemeles lives in summer, and to which it entrusts
the bringing up of its larvae.
Atemeles pubicollis resembles its summer host F. rufa
in size and colouring, and in these respects differs from its
smaller and lighter-coloured cousin, Atemeles paradoxus,
which is the guest in summer time of F. rufibarbis, also smaller
and lighter in colour. Atemeles pubicollis var. Foreli was
discovered by Forel living among Formica sanguinea in the
Vosges ; it is distinguished from pubicollis chiefly by its bright
red colour, and this colour distinguishes its host, Formica
ATEMELES PKATENSOIDES 335
sanguined, from the darker Formica rufa. A comparison
between Atemeles pubicollis and pratensoides is still more
instructive. The latter species of Atemeles was discovered by
me in Luxemburg in 1903, where it occurred in great numbers
in an isolated nest of Formica pratensis, near the old Koman
road which led from Treves to Arlon through Luxemburg.
The ants of this colony are remarkable for being very dark,
almost black, in colour, and for being covered with very
thick grey hairs ; accordingly the newly discovered Atemeles
differs from Atemeles pubicollis, that lives with Formica rufa,
in being much darker, of an almost uniform blackish brown
tint, and by having much thicker hair, especially on the lower
side of the abdomen where it curves upwards.1 I gave this
form of Atemeles the name pratensoides (resembling pratensis)
because of the remarkable likeness in colour and hair between
it and the ants that are its hosts. I was obliged to regard it
as a new systematic species, because in its colouring, structure,
and hirsute covering it differs from Atemeles pubicollis no less
specifically than pubicollis differs from other species of Atemeles.
And yet this new species of Atemeles is phylogenetically only a
highly developed instance of adaptation to Formica pratensis,
and to a very dark, hairy subspecies of pratensis. We have
therefore here a very interesting example of the origin of a
new species of inquiline, through biological adaptation to a
particular ant which is its host, under favourable local con-
ditions. These conditions are the isolated position of the
above-mentioned pratensis nest ; there are no colonies of other
species of ants in the neighbourhood, and therefore it is
impossible for Atemeles pratensoides to breed with other species
of Atemeles coming from other Formica colonies, or to meet
them in the neighbouring Myrmica nests, where Atemeles
pratensoides passes the winter and pairs in the early spring.2
1 On this subject cf. Wasmann, ' Zur Lebensweise von Atemeles pratensoides '
(Zeitschr. fiir wissenschaftl Intektenbiologie, II, 1906, parts 1 and 2) ; also
Beispiele rezenter Artenbildung bei Ameisengasten und Termitengdsten, 1906,
46 (568) &c.
2 I have frequently seen Atemeles emarginatus pair with paradoxus in my
observation nests of Myrmica. To this cross-breeding must probably be
ascribed the existence of intermediate types of formation of the prothorax
standing between the two species. (See ' Beitrage zur Lebensweise der
Gattungen Atemeles und Lomechusa,' in Tijdschrift voor Entomologie, XXXI,
1888, 29.)
336
MODEEN BIOLOGY
The formation of a peculiar kind of Atemeles, adapted to the
very dark and hairy Formica pratensis, was favoured by the
isolation of the pratensis nests in that locality ; and, by inherit-
ance and intensification of the characteristics due to adaptation,
the special variety became a subspecies, and in course of time
a species, which we now recognise as the Atemeles resembling
pratensis, or pratensoides.
The accompanying illustration (fig. 35) shows a charming
scene, drawn from nature and then reproduced by photography.
It represents an Atemeles pratensoides being fed by a large
FIG. 35. — Atemeles pratensoides Wasm. being fed by Formica pralensis Deg,
(6 times the natural size).
worker of Formica pratensis. In order to reach its hostess's
mouth, and to stroke the ant's cheeks with its forefeet as a
request for food, and to tickle her head with its antennae, as
etiquette among ants requires on such occasions, the guest had
climbed on the back of another worker-ant, somewhat smaller
in size, belonging to the same nest, which quietly allowed
itself to be used as a footstool.
In the account given of Atemeles pratensoides we have
considered the causes which may have led to the differentiation
of the species within the genus Atemeles. Let us now turn
our attention to some more general considerations which
may assist us in giving an explanation of the hypothetical
evolution of the whole Lomechusa group.
EVOLUTION OF LOMECHUSINI 337
What were the laws which governed the evolution of the
Lomechusini, and what started the process of evolution ? The
primitive form was probably one of the Aleocharinae, connected
with Myrmedonia, a genus that existed in the middle of the
Tertiary period and is preserved as fossils in amber from the
Baltic. At the present day the Lomechusa group of ant-
inquilines is sharply divided from the Myrmedonia, and no
transitional form exists to connect them, but nevertheless
there is good reason to suppose that some connecting link
between these two genera once existed.
In Schoa (Abyssinia) Antinori discovered a new species of
Staphylinidae,1 which answers very fairly to the requirements
we should make of a Myrmedonia that was in course of approxi-
mation to the form of a Lomechusa. The antennae are more
slender than in Myrmedonia, and not thickened like a string
of beads. The general shape of the body still resembles
Myrmedonia, but is decidedly broader and becoming more like
Lomechusa. The sides of the dark- coloured prothorax are
yellowish red. broad and arched as in Lomechusini ; at
the sides of the broad abdomen are small but percept-
ible tufts of yellow hair. The general colouring is blackish,
the antennae and legs being brown. Unfortunately nothing
is yet known as to the mode of life of this interesting
creature.
Let us now return to the Tertiary period, and to the evo-
lution of our Lomechusini. The hypothetical primitive form
must in its Anlage or tendency to evolution have possessed
a capacity for adaptation to a genuine guest-relationship
both in organisation and in instinct.
We may suppose that one of the Staphylinidae, being a
beast of prey and a hostile intruder like most of the Myr-
medonia to the present day, forced its company upon some
species of Formica in the Miocene epoch, and, as it possessed
this tendency to evolution and adaptation, a genuine guest-
relationship gradually grew up, which found its morphological
1 A coloured representation of the typical example of this species, that
is now in the Museo Civico di Storia Naturale in Genoa, was sent me by Dr.
R. Gcstro, who desired my opinion regarding it. The species is called Myrme-
donia mirabilis Eppelsheim. I think, however, that it ought to be considered
a distinct genus, standing between Myrmedonia and Lomechusa, and I suggest
calling it Myrmechusa.
338 MODEEN BIOLOGY
expression chiefly in the greater development of the adipose
tissue, in the growth of larger tufts of yellow hair on the sides
of the abdomen, in a modification of the prothorax, which
became broader and more curved, and in a change in shape of
the parts of the mouth and partially also of the antennae.
The increased amount of fat in the tissues made it possible
for the beetle to emit a volatile substance so attractive to the
ants5 senses of taste and smell, that they licked it off their
guests' bodies. It is in order to enjoy this substance that
the ants entertain the beetles as their guests.1 As it exudes
in Staphylinidae chiefly between the segments at the sides of
the fatty abdomen, it was at these spots that the ancestors of
Lomechusini were principally licked, and the increased stimulus
thus applied was probably the cause of the stronger develop-
ment of the patches of hair on these parts. When the ant
licks, these patches, the exudation is emitted, and the hairs
facilitate rapid evaporation. As the adipose tissue of the
prothorax takes part in the exudation, we can understand
why the prothorax has become broader and more curved, as
cavities for exudation are thus formed beside the curved
edges of the sides. Moreover, the thickening of these edges
protects the beetle against the ants' jaws. The change in the
shape of the mouth, and especially the increased breadth of
the tongue, are connected with the peculiar instinct, possessed
by these genuine inquilines, that prompts them to ask food
of their hosts by striking them with their antennae and by
stroking the sides of the ants' heads with their forefeet, and
then to take food from their mouths (fig. 35, p. 336). The
bodily modifications due to the growth of a true guest-relation-
ship among the ancestors of the Lomechusini must therefore
have been accompanied by a corresponding change in their
instincts. As the ants took most care of those guests which
emitted the fatty substance in greatest abundance, and as they
finally brought up the larvae of their friends in the same way
as their own young, they were practising a kind of instinctive
selection which I have called * Amical Selection.' 3
1 On the subject of the exudatory organs and tissues of the true inquilines
amongst ants and termites, see the work mentioned above (p. 327, n. 2),
Zur ndheren Kenntnis des echten Gastverhdltnisses, 1903.
2 Cf. Biolog. Zentralblatt, 1901, No. 23, pp. 738, &c. H. Friedmann (Die
Konvergenz der Organismen, 1904, pp. 187, &c.) has extended the idea of amical
AMICAL SELECTION 339
Natural selection, as Darwin understood it, favoured the
development of a true guest-relationship on the beetles' part.
Those individuals which were capable of resisting the rough
treatment that they originally received from the ants,1 and
which could at the same time satisfy the greed of the ants
by supplying them with the desired exudation, had undoubtedly
a decided advantage in the struggle for existence. But, on
the other hand, the same natural selection that promoted the
development of a true guest-relationship on the part of the
beetles, was opposed to it on the part of the ants, as soon as
the latter began to feed the beetles' larvae, for the larvae of the
Lomechusini are most deadly enemies to the young ants,
inasmuch as they consume the lumps of eggs and the young
larvae in masses, and finally cause degeneration in the normal
instinct of the ant to provide for its own young, so that only
deformed pseudogynes are reared. Therefore the colonies
of Formica, which showed little or no tendency to bring up
the beetles' larvae, were certainly better qualified to maintain
their existence than those in which the instinctive tendency
developed. Hence it follows that natural selection ought
never to allow the ants to bring up their worst enemies as true
inquilines. Natural selection would inevitably give preference
to those female Formica in whom that fatal instinct of the
worker-ants either did not exist, or existed in a very slight
degree. In other words, natural selection would have been
bound to oppose amical selection, as soon as the development
of a genuine guest-relationship reached a point where it became
injurious to the host. As it is, the various species of Formica
have an inherited instinct, prompting them to entertain as
guests definite species of beetles belonging to the group of
Lomechusini, and to bring up their larvae, in spite of the harm
accruing to themselves. Speaking from the point of view of
supporters of the evolution theory, we may justly say : Amical
selection has triumphed over natural selection, which, in
this case, far from being all-powerful, is powerless.
selection so as to. include Darwin's sexual selection, and seeks by means of it
to explain all the phenomena of direct convergence in the animal kingdom.
It seems to mo very doubtful whether this is possible.
1 To this day Atcmeles and Lomechusa are often violently treated by the
ants licking them, especially if the guests are old, and their exudatory tissue
is exhausted.
z 2
340 MODEEN BIOLOGY
Similar conclusions have been reached by the eminent
palaeontologist Koken, who says : l ' The Darwinian principle
of selection is not the only one to be taken into consideration,
and it appears not to be the most important. In palseonto-
logical history we often miss any suggestion of the struggle
for existence, and, on the other hand, there is often a tendency
to evolution which is not beneficial, and which occasionally is
actually injurious to society.'
6. INQUILINES AMONG THE WANDEEING ANTS
Another proof that the theory of evolution is indispensable
to an explanation of the interesting facts of myrmecophily
and termitophily is given by a number of Staphylinidae belong-
ing to the sub-family of Aleocharinae, which represent the
mimetic type of inquilines among the wandering ants (Dory-
linae) of the New and Old Worlds (figs. 36, 37). The mimicry
on the part of these inquilines is aimed at deceiving the sense
of touch possessed by their hosts, who either are blind, or have
small and simple eyes, unlike the usual faceted eyes of insects.
This mimicry culminates in producing a resemblance between
guest and host in the shape of their bodies, and especially in the
formation of their antennae ; the latter point of resemblance
enables the guests to deceive their hosts in an active, and not
merely a passive way. This remark is applicable to the
companions of the neotropical wandering ants of the genus
Eciton, as well as to those of the African Anomma and its
relatives of the genus Dorylus, that pursue their prey under-
ground.
If we compare the inquilines of the mimetic type that live
among the Dorylince in both the Old and the New World, we
shall find a remarkable similarity existing between the beetles
of this biological type that live with the Brazilian and the
African wandering ants respectively. This strange similarity
is not, however, due to a close systematic relationship between
the genera of beetles, and so does not point to there being
any direct connexion between them.
Between the genus Mimeciton (fig. 36), the highest repre-
sentative of the mimetic type living in Brazil among Eciton
1 Palaeontologie und Deszendenzlehre, 1902, p. 226.
INQUILINES AMONG DOEYLINAE 341
praedator, and the genus Dorylomimus, the highest repre-
sentative of the same biological type living in Africa among
Anomma Wilverthi, there is an astonishing likeness in
habitus, i.e. in outward appearance in general ; but closer
examination shows the likeness to depend only upon pecu
FIG. 36. — Mimeciton pulex Wasm. (S. Paulo, Brazil)
(11 times the natural size).
liarities due to adaptation, and not upon the biologically
indifferent characteristics, that are totally unlike in the two
genera. There can therefore be no question of any close
relationship between them. The same result follows from a
comparison of the inquilines of the mimetic type living with
FIG. 37. — Ecitophya simulans Wasm. (S. Catarina, Brazil)
(7 times the natural size).
various species of one and the same genus of ants, viz.
Eciton, in tropical and sub-tropical America. In this case
again there are striking resemblances in habitus, but no close
systematic relationship ; in fact, these inquilines stand so far
apart, that they actually form distinct systematic genera, such
as Mimeciton (fig. 36), Ecitophya (fig. 37), Ecitonidia, &c. How
can this surprising fact be explained ?
342 MODEKN BIOLOGY
The theory of permanence could only make this answer :
' The special genera and species of inquilines were created
simultaneously with, and expressly for, the corresponding
genera and species of their hosts ; the " harmony of the Uni-
verse " required this manifold variety on the part of the
guests, which have not adapted themselves to their hosts,
but were simply created so as to suit them.'
But why is there so great a systematic difference in the
representatives of the same biological type, even among the
species of the same genus of hosts — a difference which is
nevertheless concealed under such a strange likeness of habitus
that anyone would at once recognise an African Dorylomimus
as the double of the Brazilian Mimeciton ? The theory of
permanence can give no answer at all to this question — and
it is all the more unable to do so because we must undoubtedly
refer the systematic species within the same genus of guest-
ants, e.g. Eciton, to a common stock, from which the present
species of Eciton were differentiated by a process of natural
evolution.
Forms resembling one another so closely as Eciton Bur-
chelli (Foreli),1 and quadriglume, praedator and coecum, cannot
possibly be regarded as belonging to species originally distinct ;
and yet these species have companions, mostly guests of the
mimetic type, which generally differ widely from one another,
and occasionally even represent distinct systematic genera.
When can these guests have been created ? Their existence
in their present form would have no meaning until the parti-
cular kinds of ants, that are their hosts, had been differentiated
into their present species.
We should therefore have to assume, if we accepted the
theory of permanence, that the hosts had developed in the
course of nature, and that their guests had been subsequently
created to match them. How forced and inconsistent such
an explanation would be, must be apparent to everyone.
The theory of evolution says on the other hand : ' These
inquilines have been produced in course of time from similar,
or even from identical primitive forms, amongst which we must
1 The species formerly known as Eciton Foreli Mayr consists of the soldiers
and workers of Ldbidus Burdidli Westw. which comprises the males of the
same species. For this reason the name Eciton Foreli was changed to Burchelli.
INQUILINES AMONG DORYLINAE 343
consider especially the genus Myrmedonia, that is geologically
very old and widely distributed ; their evolution is most
closely connected with that of their respective hosts.' The
striking resemblance united with a still greater systematic
difference, which we can observe in the various genera of
inquilines of the mimetic type, is the result of an imperceptibly
slow, or rather of a progressive adaptation, occurring among
the inquilines of the various genera and species of hosts, but
on completely independent lines. The points of resemblance
are conditioned by the general laws governing the mimetic
type of inquilines among Dorylinae ; for this type it is essential
that the likeness between host and guest in the shape of their
bodies should be so great as to deceive the host's sense of
touch, and, when the mimetic type reaches its highest point,
there is a great resemblance also in the shape of their antennae.
The axiom ' when two things are equal to a third, they are
equal to one another,' enables us to account for the strange
likeness between the highest representatives of the mimetic
type of inquilines among Dorylinae in different parts of the
world. As they all resemble their hosts, they resemble one
another. The similar habitus possessed by various genera of
the mimetic type, that differ systematically (as, for instance,
Mimeciton and Dorylomimus) , is to be regarded as a ' pheno-
menon of convergence,' from the point of view of the evolution
theory. The differences, however, are due, partly to the
original difference between the primitive forms, partly to
differences in bodily formation and way of life on the part of
the genera and species acting as hosts, partly to the various
ways in which a similarity in the shape of body and antennae
can be produced, and partly to the degree of evolution of the
mimetic type to which its representatives have attained.
Here we have a real explanation of facts, an explanation that
is, of course, hypothetical in character, but is nevertheless
able to satisfy our requirements. We ought to pay particular
attention to the various degrees of evolution of the mimetic
type to which the inquilines of the same ants have attained.
The guests of Eciton Burchelli supply us with good illustrations
of these degrees^of evolution.
i The mimetic type does not stand in sharp contrast to the
indifferent type, to which belong inquilines that have retained
344 MODEEN BIOLOGY
the original form of their relatives who were not myrmeco-
philes. There are many instances in which it is doubtful
whether we ought to reckon the genus or species of inquilines
as still belonging to the indifferent type, or as having passed
over to the mimetic type. If a natural process of adaptation
has taken place, and the guests have come to resemble their
hosts, either by a series of imperceptibly slight variations or
by more sudden changes, we can easily understand that we
must inevitably meet with the mimetic type at various stages
of evolution, and the inquilines remain at each stage until
the necessity for adaptation, which varies in the case of various
forms, causes a further advance to be made.
If we compare the inquilines of the mimetic type living
among Dorylinae with those of the offensive type (Trutztypus)
FIG. 38. — Xenocephalus limulus FIG. 39. — Doryloxenus Lujae
Wasm. (Rio de Janeiro) (7 Wasm. (Congo) (22 times
times the natural size). the natural size).
(figs. 38 and 39) which belong to the systematic subfamilies
Xenocephalinae and Pygosteninae, a striking difference becomes
apparent. The forms of the mimetic type are very numerous
and differ systematically, but those of the offensive type are
remarkable for their uniformity and for their systematic like-
ness. The neotropical representatives of the offensive type
almost all belong to the genus Xenocephalus (fig. 38), and
the species of this genus, all being very much alike, live with
various species of the genus Eciton, whilst the representatives
of the same type in the Old World belong to the genera Pygo-
stenus, Doryloxenus (fig. 39), &c., which also resemble one
another very closely, and include groups of very similar species.
This peculiar morphological contrast between the manifold
forms of the mimetic type, and the uniformity of the offensive
type, admits of a very simple and natural explanation according
to the principles of the evolution theory.
The inquilines of the offensive type must possess a greater
EVOLUTION OF ANT-INQUILINES 345
aggregate of common morphological characteristics, because
adaptation aims at producing uniformity ; it has favoured
the evolution of a definite form of body, not unlike that of a
tortoise, the bending round of the head towards the protected
lower part of the creature, the shortening and thickening of
the antennae, the shortening of the legs and covering them
with bristles, &c. The result of this adaptation could not
fail to be uniform, as we see in the subfamilies known as
Xenocephalinae and Pygosteninae. But the evolution of guests
of the mimetic type was bound to be very various, for their
mimicry is designed to deceive the sense of touch in their
hosts, and naturally gave rise to forms differing widely in
degree of mimicry and in the details of its production. It is
true that we cannot do more than offer suggestions as to the
course followed in the individual cases by evolution thus
directed by adaptation, but the preceding statements are
enough to show that in this department the theory of evolution
is capable of supplying really satisfactory explanations, whilst
the theory of permanence can explain nothing at all.
Let us now compare the Eciton inquilines of tropical and
subtropical America with the Alia inquilines of the same
region. Alia and Eciton both belong to the predominant forms
of ant Fauna in the tropics of the New World, and these two
genera have stamped their peculiarities on all the other ants ;
they also play a most important part in the struggle for exist-
ence, Eciton as prevailing over other insects, and Atta over
plants, for the Eciton are wandering robber-ants, and the
Atta destroy leaves and grow fungi. The former, as a rule,
have no permanent nests, but the latter construct huge nests
stretching far under the ground, where they employ the
fragments of leaves, that they have carried in, for cultivating
a kind of fungus (Rozites gongylophora) , which they use as
food for themselves and their young. As the Staphylinidae
make their homes preferably in decaying vegetable matter,
we should expect the number of exclusively attophile genera
to be much greater than that of exclusively ecitophile genera
of the same family of beetles. We should be all the more
justified in this supposition as the inquilines in the Atta nests
run much less risk of being eaten by their hosts than do those
living with the wandering robber-ants. If, therefore, the
346 MODEEN BIOLOGY
guests were originally created expressly for their respective
hosts, we should find a great many specially attophile genera
of Staphylinidae and very few ecitophile.
But what are the facts ? They show us a state of affairs
that is the direct opposite of this supposition. Of the twenty-
one genera of Staphylinidae known at the present time which
contain species living with Eciton, there are twenty genera
consisting exclusively of Eciton inquilines, and only one genus
(Myrmedonia) which includes, besides ecitophile species,
others living partly with other ants, and partly not with ants
at all. On the other hand, there are about twelve genera
of Staphylinidae containing Atta inquilines, and only two of
these (Attonia and Smilax) are exclusively attophile, whilst
all the rest include, besides the attophile species, others which
live either with other ants, or not with ants at all. These facts
speak plainly enough. They show us that the different dis-
tribution of the Atta and Eciton inquilines depends upon the
laws of adaptation. Precisely because the wandering ants
are rapacious and extraordinarily active robbers, do they
have so many peculiar genera of guests, that have adapted
themselves to the ants, not merely lest they should be destroyed
by them, but also in order to share their booty by allying them-
selves with the robbers.
And precisely because the Atta are peaceful destroyers of
leaves and growers of fungi, do they have so few peculiar
genera of guests, in spite of the favourable conditions which
the Atta nests offer to the existence of Staphylinidae. The law
underlying this apparently paradoxical phenomenon may be
expressed as follows in biological language : — Inquilines among
Eciton are under a much greater necessity for adaptation than
those among Atta. This greater necessity for adaptation led to
increased frequency in its occurrence, and to a higher degree in
its attainment, on the part of Eciton inquilines as compared
with Atta inquilines.' The theory of evolution can account
for this law, but the theory of permanence cannot, for it admits
of no modification by adaptation in the systematic species.
It really seems to me that the theory of evolution is not only
attractive, as supplying an explanation of facts of this kind,
but that it alone is capable of giving a completely satisfactory
explanation, although we may not be in a position to describe
EVOLUTION OF ANT-INQUILINES 347
the processes of evolution as exactly as we were able to do
with regard to the differentiation of the species of Dinar da.
A few words must be added on the subject of the laws that
governed the evolution of Dorylinae inquilines of the mimetic
type.
The external influence directing the various methods of
evolution, which finally culminated in such extreme forms
as Mimeciton, Ecitophya, Dorylomimus, Dorylostethus, &c.,
was probably supplied by natural selection, as, among the
companions of the wandering ants, those would be most
favourably circumstanced which were able to deceive the
ants' sense of touch by resembling them in shape and especially
in the formation of their antennae. They were not only better
protected against attacks on the part of their hosts, but were
able to seize a larger share of their booty, consisting chiefly
of insects, and incidentally to consume the young of their hosts
with impunity. Natural selection alone cannot, however,
account for the existence of these methods of evolution, for
the material, upon which selection acted, must have been
furnished by the already existing tendency possessed by these
genera of beetles to adopt certain forms. On the other hand,
we must not interpret these tendencies merely in the sense
of general laws of growth, as Eimer's orthogenesis does, for
tne laws of growth governing the original primitive forms of
these genera of beetles could not differ much from those govern-
ing their nearest systematic relatives belonging to the family
of Staphylinidae. The general laws of growth of the Staphy-
linidae supply no sufficient explanation of the fact that the
inquilines of the mimetic type have differentiated themselves
into so many different genera, that are systematically unlike
each other and unlike the primitive forms from which they
are descended ; we must therefore assume that the capacity for
evolution possessed by the earliest forms was influenced and
modified by the internal power of adaptation to new biological
conditions, so that spontaneous departures from the original
form occurred, tending to produce the mimetic type, but this
tendency took different directions according to the various
genera and species of the creatures amongst which the inquilines
lived. The further development of these tendencies to evolu-
tion cannot have been the result of a gradual accumulation of
348 MODEKN BIOLOGY
innumerable quite trifling variations, as Darwinism maintains,
for in that case hundreds of thousands of years would have
been required for the production of a single genus such as
Mimeciton. In the struggle for existence minimum variations
are of scarcely perceptible advantage, as they would not enable
the guests to deceive the ants' sense of touch. We are there-
fore forced to believe that the evolution of inquilines of the
mimetic type took place by a series of more or less rapid
transitions, after the fashion suggested by the mutation theory.
Here again Darwin's theory of selection proves to be as unsatis-
factory as the directly opposed theory of orthogenesis, put
forward by Eimer. I am of opinion that the real solution of
this puzzling process of evolution is to be sought in the inward
power of adaptation, possessed by the living organism, which
power can react beneficially under external stimulus, and can at
the same time retain, and perpetuate by transmission, the bene-
ficial modifications once adopted, and even carry them further.
I ought to point out that in Mimeciton (fig. 36, p. 341)
especially there are certain peculiarities which are explicable
neither by natural selection nor by the general laws of growth,
such as the change of the faceted eyes into simple ocelli, re-
sembling the simple eyes of its host, Eciton praedator, but
situated in the hollow at the base of the antennae. This
' excessive mimicry ' in the formation of the eyes in Mimeciton
is the more remarkable, as the beetle often accompanies the
ants on their marches even by daylight. It gives the impres-
sion that the tendency to evolution of a mimetic type has
here exceeded the limits of what is beneficial, as if the process
once begun could not be arrested. Brunner von Wattenwyl
has given this phenomenon the name of Hypertely.
Let us now go back to our comparison between the theories
of permanence and descent.
7. TRANSFORMATION OF WANDERING ANTS' INQUILINES
INTO TERMITE-!NQUILINES.
(See Plate III, figs. 1, 2)
Some years ago two correspondents of mine in India, Father
Heim, missionary in the Ahmednagar district, and Father
Assmuth, Professor at St. Francis Xavier's High School in
A TEKMITOPHILE DOKYLOXENUS 349
Bombay, made an interesting discovery. They found in the
nest of an Indian species of termite (Termes obesus Kamb.) a
number of very remarkable inquilines, and amongst them a
little beetle of the family of Staphylinidae, belonging to the
subfamily Pygosteninae, and to the genus Doryloxenus. This
genus represents the most perfect instance of the offensive
type of inquiline among the Dorylinae of the Old World (cf.
fig. 39, p. 344 and Plate III, figs. 1, 2). The tiny creature's
spindle-shaped body, that the ants' jaws cannot seize, its short,
thick, horn-shaped antennae, and especially its extremely short
legs, the tarsi of which are all atrophied and transformed
into prehensile organs — all these morphological peculiarities
point to a life among wandering ants rather than among
termites. Moreover, all the other species of the genus Dory-
loxenus, as far as their mode of life is known, are actually
inquilines among the African wandering ants Dorylus and
Anomma. Our new termite-inquiline so much resembles
Doryloxenus Lujae (see fig. 39, p. 344), from which it differs
chiefly in being bigger (2 mm.), that we need only compare the
photograph of it (Plate III, fig. 1) with fig. 39, in order to
recognise the likeness between them. I have given also on
Plate III, fig. 2, an illustration of the forefoot of Doryloxenus
highly magnified. It is stumpy, not jointed, and covered
with long spines and numerous delicate, white, tenent hairs,
shaped like funnels, which enable the little beetle to cling
to the young of the ants or even to the ants themselves, so
that it actually rides when it accompanies the long-legged
nomadic ants on their expeditions.1
My surprise at discovering a termitophile Doryloxenus in
India is therefore easily understood. How was it possible that
a beetle, whose whole structure proclaims it to be a guest of
the wandering ants, and the other members of whose genus
actually ride on the ants in Africa, should in India live as a
recluse in the clay- dwellings of the termites ? When I received
the first consignment of Indian termite-inquilines, and found
this beetle amongst them, I thought one of my correspondents
had made a mistake ; I wrote at once to say that he must
1 Father H. Kohl recently found two distinct species of Doryloxenus riding
on ants in the Upper Congo, and Luja caught another species on the Zambesi,
also riding on an ant thatliad just crossed a brook. (Cf. Zur ndheren Kenntnis
der Odste der Treiberameisen, &c., pp. 650, 667.)
350 MODEEN BIOLOGY
have put accidentally an inquiline of the Indian wandering
ants into a glass containing termites. But the mistake was
on my part. Further parcels sent by my two correspondents
showed beyond a doubt that the new Doryloxenus was quite a
usual, and even a frequent guest among the termites both in the
Ahmednagar district and in Bombay. What is the solution of
this biological problem ?
The only possible solution seems to me to be the following :
In India the wandering ants of the subfamily Dorylinae at the
present time no longer play so important a part biologically
as in Africa. It is probable however, that long ago, when in the
Tertiary period India and Central Africa were still united and
formed a continuous Indico-African continent, the condition
of India more closely resembled the present condition of
Africa, and in the struggle for existence in the insect world the
wandering ants in India were of as great importance as they
are now in Africa. The StapJiylinidae, which had adapted
themselves to be inquilines of the offensive type among these
ancient Dorylinae, and thus had developed into a distinct
systematic subfamily (Pygosteninae) , were doubtless in India
also originally the guests of wandering ants exclusively, for
no other reason can be given for their characteristics due to
adaptation, and especially for those of the genus Doryloxenus.
What took place when India was separated from Africa, and
the biological importance of the wandering ants there gradually
diminished, so that at the present day in India no Dorylinae
occur that organise extensive predatory expeditions above
ground ? l
This biological change could not fail to influence the guests
of these Indian Dorylinae, which share in the expeditions of their
hosts and live on their booty. Many of these guests would no
doubt find it expedient to seek another refuge. But whither
could they go ? The wandering ants are fond of attacking and
plundering the nests of termites, as the latter with their
soft skin can offer but slight resistance to the jaws of the
ants, and fall an easy prey to them ; 2 and their guests
1 Dorylinae of the genera Dorylus and Aenictus living underground are still
common in India.
2 This statement is confirmed by E. Luja's observations on the Lower
Congo. He found colonies of a Dorylus living underground (D. fulvus-dentifrons)
A TEKMITOPHILE DOKYLOXENUS 351
accompany the Dorylinae on these raids, as they still do in the
tropics.
We need only suppose that some individuals of an Indian
species of Doryloxenus were left behind in a nest of Termes
obesus, when it was stormed by the ants, and became the
ancestors of a new termitophile species of Doryloxenus. These
little predatory beetles would find plenty of food amongst
the young termites ; their inherited offensive type was no
longer as necessary as before, but it gave them a more than
sufficient protection against the jaws of the warriors and
workers of their hosts under their new circumstances. Their
short legs, with tarsi transformed into prehensile organs, could
not be any disadvantage to them in the company of termites,
in fact they were useful in the distribution of the species, as
the beetles could more easily cling to the winged termites ;
when these swarmed out of the parent nest to form new colonies
This explains why the peculiar formation of tarsi in Doryloxenus
was retained by the new termitophile species.
This is roughly the hypothetical phylogeny of this interest-
ing Indian Doryloxenus, which I regard as a deserter from the
company of the wandering ants ; that is why I have given it
the name Doryloxenus transfuga.
Some one may feel inclined to say that this biological
metamorphosis, by which an inquiline of the wandering ants
is assumed to have become the guest of termites, sounds like a
story from the Arabian Nights ; it might, perhaps, be compared
with some edifying tale from an old Buddhist collection of
legends, in which a robber, attacking a peaceful monastery of
Bonzes, was converted and remained in the monastery in order
to atone for the sins of his previous companions in wrong-
doing. Nevertheless, it would be hard to find any other
natural explanation, than that suggested above, for the fact
that there are in India beetles of the dorylophile genus Dory-
loxenus habitually living as inquilines among termites. The
theory of permanence offers no solution for this problem. We
have therefore to choose whether we shall regard it as an
at the foot of termite nests (Acanthotermes spiniger-Lujae) and occupied in
plundering them. Cf. Zur ndheren Kenntnis der Gdste der Treiberameisen,
p. 673. Father H. Kohl has recently made similar observations on the Upper
Congo.
352 MODEEN BIOLOGY
incomprehensible natural ' freak,' or acknowledge that in
India, within a comparatively short space of time, part of the
genus Doryloxenus has changed its hosts, and from being an
inquiline of wandering ants, it has transferred its quarters to
the termites. If such a change can take place, although the
modes of life of Dorylinae and termites are totally different,
or rather diametrically opposed, there is no great difficulty
in assuming that the inquilines of ants and termites may have
been produced from forms which were originally neither
myrmecophile nor termitophile, but have adapted themselves
to their hosts by a more or less lengthy process of evolution.
In the case of Doryloxenus transfuga the change in its
mode of life has not been accompanied by any great morpho-
logical modification ; as a termite-inquiline the beetle has
remained almost the same as it was when a Dorylinae inquiline.
This is explicable for two reasons — firstly, the change of host
did not necessitate any rapid alteration in the characteristics
already acquired by adaptation, because the beetle was fairly
well suited to its new way of life ; and, secondly, its migration
from the company of the wandering ants to that of the termites
took place after the Tertiary period, i.e. not long ago, from a
geological point of view.
Before quitting the subject of Doryloxenus transfuga, I must
allude to some confirmations of and addition^ to the hypothesis
just laid down.1
Other sample nests, subsequently sent from India by
Father Heim and Father Assmuth, revealed the surprising fact
that not only one, but two specifically distinct forms of Dory-
loxenus inhabit the nests of Termes obesus and its subspecies
T. wallonensis (Doryl. transfuga [cf. fig. 40 and Plate III, fig. 1]
and termitophilus) ; in some nests they are very numerous, but
they are found chiefly near the young of the termites and in
their fungus beds ; in this respect they resemble Termitodiscus
1 For the bibliography of the subject see the following works mentioned on
p. 327, note 2. Termiten, Termitophilen und Myrmekophilen aus Ceylon,
p. 158 ; Zur naheren Kcnntnis der Gdste der Treiberameisen, pp. 614-616, and
651, 652. (A description of the two termitophile species of Doryloxenus and of
the new genus Discoxenus with its two species may be found in the latter work,
pp. 654-656) ; ' Die phylogenetische Umbildung ostindischer Ameisengasto in
Termitengaste ' (Compt. Rend. d. Ill Congr. internal, de Zoologie, Berne, 1904,
pp. 436-448, with plates) ; Beispiele rezenter Arteribildung bei Ameisengdsten und
Termitengdsten, 49 (571) &c.
A TEEMITOPHILE DOKYLOXENUS 353
Heimi and the species of Discoxenus to which I shall refer
later on.
This fact is a conclusive confirmation of the occurrence of
species of Doryloxenus in the termite nests of Central India,
round Ahmednagar and Bombay, and it completes the account
given of their termitophile adaptation.
A close examination of the two kinds of Doryloxenus showed
that in spite of their having retained the characteristics of
their dorylophile adaptation, which they have in common with
African species of the same genus living with Anomma and
FIG. 40. FIG. 41. FIG. 42.
FIG. 40. — Doryloxenus transfuga Wasm. (India) (15 times the natural size).
FIG. 41. — Discoxenus lepisma Wasm. (India) (15 times the natural size).
FIG. 42. — Termitodiscus Heimi Wasm. (India) (15 times the natural size).
Dorylus, they differ from the latter in several respects, especially
in their hairy covering, in the formation of the surface of the
body and in the structure of the head. The front part of the
head is deeply depressed, as if it were about to turn over to
the lower part of the body, as is actually the case in the genera
that I am about to mention. Among the inquilines discovered
by Father Heim and Father Assmuth in the same termite nests
there is also a new genus of Staphylinidae, which I described
recently, and called Discoxenus (fig. 41). In shape it shows
a curious cross between the conical body of Doryloxenus (fig.
40) and the orbicular form of Termitodiscus (fig. 42). This
new genus Discoxenus contains two distinct species : Discoxenus
lepisma (fig. 41) and Assmuthi. The remarkable feature in this
new genus is that it stands (as may be seen from figures 40-42)
2 A
354 MODEEN BIOLOGY
exactly midway between the genera Doryloxenus (fig. 40) and
Termitodiscus (fig. 42), of which the latter represents the most
perfect instance of the offensive type occurring among termi-
tophile Staphylinidae in India, for the body is round and flat,
and affords complete protection to the short extremities of the
creature.1
In Discoxenus (fig. 41) the abdomen is still conical as in
Doryloxenus (fig. 40), but the front part of the body is already
broad and flat, as in Termitodiscus (fig. 42). The head is on
the lower side of the pro thorax as in Termitodiscus (fig. 42),
but the long spindle-shaped antennae still resemble those of
Doryloxenus (fig. 40), and project from below the head, whereas
in Termitodiscus they are very short, broad, and flattened
down. In Discoxenus the feet have normal tarsi with four
joints as in Termitodiscus, and are not like those of Dory-
loxenus in having but one joint and being metamorphosed
into prehensile organs. Discoxenus is therefore, from the
point of view of comparative morphology, a transitional form
between Doryloxenus and Termitodiscus.
We have then good reasons for assuming that the Indian
termite-inquilines of the genus Termitodiscus are descended
from ancestors resembling Discoxenus, and these again from
others resembling Doryloxenus. In other words : The evolu-
tion of the offensive type of Indian termitophile Staphylinidae,
which culminated in Termitodiscus, probably began among
relatives of Doryloxenus, which entered termite nests in the
course of predatory expeditions made by the wandering ants.
The termites, therefore, had to thank these ants for having
brought them not only Doryloxenus, but also the beautiful
genera Discoxenus and Termitodiscus, as these inquilines were
of common origin with Doryloxenus.
The process of adaptation, which has resulted in the evolution
of the present genus Termitodiscus from ancestors that were
once guests of the wandering ants, would thus seem to have
passed through three different stages ; in the first of which
there was a likeness to Doryloxenus, in the second to Discoxenus,
and in the third Termitodiscus assumed its present form. But
1 For the description of Termitodiscus Heimi see my work : ' Neue Termito-
philen und Myrmekophilen aus Indien ' (Deutsche Entomologische Zeitschrift,
1899, I, 145-180, Plates I, II), p. 147 with Plate I, fig. 1.
EVOLUTION OP TERMITE-INQUILINES 855
X
we must beware of regarding this hypothetical process as
consisting of a real series of forms in which our present Termi-
todiscus is the direct descendant of Discoxenus, and Discoxenus
of Doryloxenus. We ought rather to regard the process of
evolution as composed of three quite distinct processes of
adaptation, taking place in different geological periods and
absolutely independent of one another.1
One proof of this is the fact that Doryloxenus has quite
rudimentary tarsi, and the other two genera have normal.
A form with normal tarsi can never be genetically descended
from one with rudimentary, but the reverse must be the
case. Therefore the earliest ancestors of Discoxenus and
Termitodiscus must still have had normal tarsi ; they cannot
have been genuine Doryloxenus for this reason, but older
relatives of this genus, whilst its tarsi were not yet rudi-
mentary. Further, as we at the present day find the three
genera Doryloxenus, Discoxenus, and Termitodiscus together
in the same termite nests in India, from the standpoint of the
theory of evolution we are forced to assume that relatives
of Doryloxenus became termite-inquilines in three different
epochs. From the last of the three date both the Indian
species of termitophile Doryloxenus ; this transition must,
as I have already said, have taken place comparatively
recently, perhaps during the Pleistocene epoch, as these
species still retain the characteristics due originally to dory-
lophile adaptation. The genus Discoxenus, which differs
greatly from Doryloxenus, was produced in the second transi-
tional epoch, and this is geologically anterior, and belongs
perhaps to the end of the Tertiary period. The first and
earliest transition, of which the present genus Termitodiscus is
the product, is still more remote geologically, and belongs
perhaps to the middle of the Tertiary period ; for the genus
Termitodiscus, in spite of having many points of resemblance
to Discoxenus, displays a much more advanced evolution of
the termitophile offensive type. The remote antiquity of
this first transition of relatives of Doryloxenus to the termito-
phile mode of life is borne out by the fact that in South Africa
1 For further information on this subject see the lecture mentioned on
p. 352 : ' Die phylogenetische Umbildung ostindischer Ameisengaste in
Termitengaste.'
2 A 2
356 MODERN BIOLOGY
there are also two species of Termitodiscus (T. splendidus
and Braunsi) living with two different species of termites
(Termes vulgaris and transvaalensis) , whilst the genus Disco-
xenus is not yet known to occur in Africa, nor have any
termitophile species of Doryloxenus been discovered there
hitherto. It is possible that further research will fill these
gaps in African Fauna. In any case we must assume that
the earliest of the three transitions mentioned above, in
which the genus Termitodiscus was produced, took place
before India and Africa were completely separated ; l otherwise
we cannot account for the fact that the genus Termitodiscus
is common to both continents. If we grant this, we assume
that the earliest transition was common to Africa and India,
but that the other two transitions of relatives of Doryloxenus
to the termitophile life occurred only in India.
From the biological standpoint there is no more difficulty
in assuming a repeated transition than an isolated instance
of transition, and the existence in India of two termitophile
species of Doryloxenus affords us very weighty grounds for
believing this to have occurred.
It is plain that the relationship between the Indian species
of Doryloxenus found in termite nests, and the allied members
of the same genus which accompany the wandering ants,
possesses a degree of probability bordering on certainty,
and far higher than the relationship between Discoxenus and
Doryloxenus, although this in its turn is more probable than
the relationship between Termitodiscus and the connexions of
Doryloxenus through Discoxenus. The greater the systematic
difference between the forms in question, the weaker are
the reasons for assuming that they are of common origin.
(See Chapter IX, p. 291.) Nevertheless, we may still regard it
as very probable that the Indian and African inquilines of the
offensive type, belonging to the class of termitophile Staphyli-
nidae, represented by the genera Termitodiscus and Discoxenus,
may be traced back phylogenetically to the intrusion oiDorylinae
inquilines into termite nests, in the course of predatory expedi-
tions made at various times by the wandering ants.
1 In the middle of the Tertiary period both ant and termite fauna were
already highly developed, and most of our present genera existed, so that
there are no palseontological difficulties in the way of this assumption.
PYGOSTENUS TEKMITOPHILUS
357
I stated this hypothesis at the Sixth International Congress
of Zoologists at Berne, in August 1904, since which date it
has received very interesting confirmation from a new discovery
made in tropical Africa, of which a short account must be given.1
In the nests of an African termite which erects peculiar,
fungus-shaped structures, Eutermes (Cubitermes) fungifaber
Sjost., at Sankuru on the Lower Belgian Congo, in January
1905, Edward Luja discovered a new termitophile species
of the genus Pygostenus, which otherwise lives with the African
wandering ants, Dorylus and Anomma, and is closely related
to Doryloxenus, and belongs to the same subfamily Pygostenini.
FIG. 43. — Pygostenus pubescens
Wasm. (Congo) (10 times the
natural size).
FIG. 44. — Pygostenus termito-
pkilusW&sm. (Congo) (12 times
the natural size).
I described the new species, giving it the name Pygostenus
termitophilus.
It is distinguishable from the dorylophile members of the
same genus by being more glossy, and by having a less
clumsy structure and no hairs on the abdomen ; only the
tips of it show the usual ring of black bristles. The antennae
are longer and the head more arched than in Anomma inqui-
lines of the same genus. In order to show these points of
difference very clearly, I have given illustrations of Pygostenus
pubescens (fig. 43), which lives with Anomma Wilverihi near
the Congo, and of Pygostenus termitophilus, side by side,
both greatly magnified. The new termitophile Pygostenus
is marked off from the dorylophile members of the same
genus by differences analogous to those which we observed
in the Indian termitophile Doryloxenus ; the modification
1 For fuller details see Beispiele rezenter Artenbildung, 51 (573) &c.
358 MODEEN BIOLOGY
in the form of the head is, however, comparatively slight in
comparison with that undergone by the latter genus.1
There is, therefore, in tropical Africa at least one termito-
phile species of Pygostenus, which may be compared with the
Indian Doryloxenus, and for whose origin we may account
in an analogous way. We must assume that this creature,
now an inquiline among termites, was once a guest among
wandering ants, for the whole structure of Pygostenus is
that of the genuine offensive type of Dorylinae inquilines,
and the other species of the genus — we already know about
twenty — are all companions of the wandering ants in Africa.
Pygostenus termitophilus was not specially created to live
with the termites, but it has adapted itself to a termitophile
existence ; it is like Doryloxenus transfuga, a deserter from
the company of the wandering ants.
The genus Pygostenus represents a decidedly offensive
dorylophile type, but one not so highly developed as that
of Doryloxenus. The body is less like a spindle in shape,
and the tarsi are normal and have not become prehensile.
The latter point is particularly important. It explains why
the Pygostenus accompany their hosts on foot, whereas the
Doryloxenus ride on their backs. Father Hermann Kohl,
C.SS.C. has actually observed both these facts on the Congo.
The Indian Doryloxenus, which have become termite-inquilines,
became associated with their new hosts through falling off
the ants' backs in the course of a raid upon the termites,
and being left behind in the termite nests. The transition
to a termitophile existence in the case of the African Pygostenus
was probably the result of the little beetles' losing sight of
the ants during an expedition, and seeking refuge in neigh-
bouring termite nests. Their offensive type would facilitate
their securing admission, as the jaws of the termites could
not do them so much harm as those of strange ants. When
the new guests were naturalised among the termites, a
morphological transformation gradually followed, so that in
time they became a new termitophile species, viz. Pygostenus
termitophilus.
1 There is perhaps a second very small species, Pygostenus infimus Fauv. in
Gaboon, which is also termitophile, as its shape approximates very closely to
that of Pyg. termitophilus, but unfortunately we do not yet know precisely
where it was discovered.
EVOLUTION OF TEKMITE-INQUILINES 359
As the genera Pygostenus and Doryloxenus are systematically
very closely related, and as the former represents a lower
stage of evolution of a dorylophile offensive type than the
former, it is probable that the above-mentioned connexions
of Doryloxenus, from which we imagined the termitophile
genera Discoxenus and Termitodiscus to be descended, had
more resemblance to Pygostenus than to Doryloxenus. This
is certainly true of the tarsal formation of the earliest deserters ;
the tarsi must have been normal, as they are still in Pygostenus,
Discoxenus and Termitodiscus, and not rudimentary, as they
are in Doryloxenus at the present time.
Let us now sum up the results of our consideration of the
way in which, both in India and in Africa, beetles that once
lived among wandering ants have become termite-inquilines.
1. That Staphylinidae of the dorylophile offensive type of
Pygosteninae have passed from the company of wandering
ants into that of termites, and in adapting themselves to
a termitophile existence have formed new systematic species,
has occurred at least twice in the Quaternary period; once
among the African species of the genus Pygostenus, and once
among the Indian species of the genus Doryloxenus.
2. The occurrence of these two transformations of ant-
inquilines into termite-inquilines we may regard as absolutely
proved by facts, for otherwise we can discover no natural
explanation of the existence of these isolated termitophile
species among the numerous dorylophile species belonging to
the same genus. The whole type of the genus is decidedly
dorylophile, both in Pygostenus and Doryloxenus.
3. From these two comparatively recent transformations
of ant-inquilines into termite-inquilines we deduce the hypo-
thetical conclusion that two other transformations took
place at an earlier date, in the Tertiary period, which resulted
in the production of our present termitophile genera, Disco-
xenus and Termitodiscus, probably by a similar process,
i.e. by the passing over of beetles, that had previously lived
with wandering ants, to a termitophile existence. Of these
two hypothetical transitions, we must believe that the later —
that of Discoxenus — took place in India, the earlier — that
of Termitodiscus — in the Africo-Indian continent.
4. The termitophile species of the genera Doryloxenus
360 MODEKN BIOLOGY
and Pygostenus may be regarded as direct evidence of a recent
formation of species, whilst the termitophile genera Discoxenus
and Termitodiscus supplement this evidence, and enable us
to extend it to the explanation of the origin of new genera.
8. THE FAMILY OF CLAVIGERIDAE
(See Plate III, figs. 3-6)
Let us now turn to the family of the Clavigeridae (Plate
III, figs. 3, 5, 6), and see what support they can give to the
theory of evolution or to that of permanence.
The little yellow Claviger testaceus Preyssl. (Plate III,
fig. 3) is the genuine ant-inquiline, whose way of life has been
known to us longer than that of any other similar creature
among our native Fauna. As long ago as 1818, P. W. J.
Miiller1 published his classical observations regarding the
relations existing between this beetle and the little yellow
field- ant (Lasius flavus) ; but we may remark incidentally
that in spite of our long acquaintance with Claviger testaceus,
we still do not know where and how its larvae live. Its
relatives already number over a hundred described species,
belonging to every part of the world and divided into about
thirty distinct genera. All the members of this family are
genuine ant-inquilines, hospitably entertained by the most
widely differing varieties of ants. At the end of the book
the reader will find a photographic reproduction of our native
Claviger testaceus (Plate III, fig. 3), and also of two very
remarkable Clavigeridae from Madagascar, Paussiger limicornis
(fig. 5) and Miroclaviger cervicornis Wasm. (fig. 6). The last
is the largest member of the whole family, and is 4 mm. in
length ; a giant among its kinsfolk, and distinguished by its
antennae shaped like antlers.
The appearance of all the Clavigeridae proclaims them to
be genuine inquilines (cf. Plate III, figs. 3, 5, 6). All the
species are bright reddish yellow or red, and glisten with
fat, thus possessing the true symphilic colouring of genuine
inquilines ; they have stunted antennae, and the number
of joints in them is considerably reduced.
1 ' Beitrage zur Naturgeschichte der Gattung Claviger ' (Germars Magazin
der Entomologie, III, 1818, pp. 69-112).
CLAVIGEKIDAE 361
At the base of the abdomen, the first segment of which
is larger than all the others together, they have a more or less
extensive hollow or pit for exudation, surrounded or almost
concealed by the tufts of yellow hair on the base of the abdo-
men and the tips of the wing-sheaths (cf. especially Plate III,
fig. 6). All these family characteristics of the Clavigeridae,
which distinguish them from their nearest systematic con-
nexions, the Pselaphidae, are due solely to their adaptation to
the position of true inquilines. As a representative of the
Pselaphidae we may take Pselaphus Heisei, whose photograph
will be found on Plate III, fig. 4. This beetle has very long
and highly developed maxillary palpi, but among the Clavi-
geridae they are greatly stunted, the reason fox this being
that the long palpi are useful to creatures seeking and ex-
amining their own food, but they would be useless to the
Clavigeridae, which are fed by their hosts, and so are relieved
from the necessity of procuring food for themselves. The
number of joints in the antennae of Clavigeridae is much less
than in those of the Pselaphidae , because the former use their
antennae chiefly as a means of communication with the ants,
and so it is convenient for the antennae to be short and strong ;
they are often shaped like a sceptre, a baton or a club (cf.
Plate III, fig. 4 with figs. 3, 5, 6), whence the name Clavigeridae,
clava — club. A diminution in the number of joints in the
antennae increases the force of the blows that they can give,
as they are less pliable when they have fewer joints ; and as
the ants often seize their tiny guests by the antennae and
drag or carry them away, the reduced number of joints in the
antennae renders them less liable to be broken off. The tufts
of yellow hair and the pit at the base of the abdomen in Clavi-
geridae are unmistakably characteristics due to adaptation
(see Plate III, figs. 3, 5, 6),1 for these hairs assist in the emission
of the substance that is so attractive to the ants as to make
them lick their guests to obtain it. It is probably some kind
1 On the photograph of our little yellow Claviger (Plate III, fig. 3) the
large tufts of yellow hair at the points of the wing-sheaths can hardly be seen.
They are quite visible, however, on the photograph of the staghorn beetle
from Madagascar (fig. 6) ; two large tufts of yellow hair screen the semi-
circular exudatory hollow at the base of the abdomen ; two other tufts are
situated on each side at the point of the wing-sheath, and a row of small
hairs runs round the side edge of the abdomen, and even the feelers have rings
of stiff yellow bristles round their lower half.
362 MODERN BIOLOGY
of ether derived from fat, or some other volatile product of the
adipose tissue and peculiar glandular tissue lying immediately
beneath the hairs.1
In the same way the beetle's glossy yellow colouring is a
direct result of its possessing a great abundance of that exuda-
tory tissue, which is anatomically the foundation of its position
as a true inquiline. Finally, the remarkable enlargement of
the first free segment of the abdomen is connected with the
same fact, as, the larger this segment is, the larger can the
exudatory hollow belonging to it become. We are therefore
fully justified in saying that all the systematic characteristics
distinguishing the Clavigeridae from the Pselaphidae prove
on examination to be simply due to their adaptation to the
position of genuine inquilines.
Now there are a number of transitional forms connecting
the Clavigeridae and the Pselaphidae, so that in many exotic
genera of the latter we can trace a striking approximation to
the former family. For this reason Raffray2 and others
regard the Clavigeridae as merely a systematic subfamily of the
Pselaphidae, although the typical Clavigeridae are extremely
unlike the typical Pselaphidae.
Viewed from the standpoint of the theory of evolution
this is all quite intelligible. If the Clavigeridae originally
branched off from the Pselaphidae, it was by way of progressive
adaptation. The various genera of Clavigeridae are so many
stages or modes of adaptation on the part of former Pselaphidae
to the position of inquilines among ants. But the theory of
permanence is incapable of assigning any reason for the above-
mentioned morphological phenomena. It simply accepts
them as facts, and assumes that the various genera and species
of Clavigeridae, like their normal hosts, were all originally
created exactly as we see them to-day. This hypothesis is
supposed to exalt the wisdom and power of the Creator, but, in
my opinion, they are revealed in a fairer light, if we accept the
theory of evolution, and believe that the wonderfully manifold
and beneficial morphological and biological peculiarities of the
1 For a more precise anatomical and histological examination of the exuda-
tory tissues in Claviger testaceus see * Zur naheren Kenntnis des echten Gast-
verhaltnisses ' (Biolog. Zentralblatt, 1903, No. 5, pp. 201-206).
2 « Genera et Catalogue des Pselaphides ' (Annales de la Societe Entomologique
de France, 1903-1904).
CLAVIGEKIDAE 363
Clavigeridae are real adaptations to the genuine guest-relation-
ship, brought about by natural causes.
The theory of evolution will not be able to tell us much
regarding the precise manner in which the genera and species
of Clavigeridae have been evolved, until we have a complete
knowledge of the mode of existence of all the Clavigeridae of
the present time, and of their special relations to the ants
that are their respective hosts, and until we have, moreover,
discovered all the extinct representatives of the same family
as fossils. It would be unreasonable to require the theory of
descent to account for the origin of genera and species, in the
present state of our knowledge. We may remark incidentally
that we already know one of the Pselaphidae (Tmesiphoroides
cariniger Motsch.), belonging to the middle of the Tertiary
period and found in the Baltic amber in East Prussia,1 which,
by having antennae with a reduced number of joints, appears
to be a transitional form standing between the true Pselaphidae
and the true Clavigeridae.
If we are asked to account phylogenetically for the extra-
ordinary antler-shaped antennae of Miroclaviger cervicornis
(Plate III, fig. 6), that bear no resemblance to the ordinary
club-shaped antennae of other Clavigeridae, we may reply
that this kind of beetle lives with some very large ants in
Madagascar (Camponotus Radamae var. mixtellus For.) ; the
elongation of its antennae is probably due to its living with
such long-legged hosts ; if it is to reach the ants' heads and ask
for food, it needs very long antennae. This does not, however,
explain their remarkable shape, for which at present no reason
can be suggested, although the same antler-like formation
occurs in another of the Clavigeridae of Madagascar (Apoderiger
cervinus Wasm.) as well as in several Paussidae in the same
island, viz. Paussus dama Dohrn, (Plate IV, fig. 6), elaphus
Dohrn and cervinus Kr. Why in Madagascar the ant-inquilines
belonging to various families of beetles have antennae tending
to resemble antlers, is one of those problems in animal geography
for which biology has hitherto found no solution. It is certainly
no mere freak of nature, although we cannot account for this
1 Cf. von Motschulsky, fitudes Entomologiques, V, 1856, p. 26 with plate,
fig. 5. Cf. also W. L. Schaufuss, 'Preussens Bernsteinkafer ' (Pselaphiden)
(Tijdschr. voor Entomologie, XXXIII, 1890, 1-62), pp. 13, &c.
364 MODEKN BIOLOGY
strange phenomenon. However, it does not affect the result
to which our previous considerations led us, according to
which we regard the Clavigeridae as phylogenetically descended
from Pselaphidae, the differences between them being due to
a gradual, or perhaps a somewhat rapid, process of adaptation
to the conditions of life of true inquilines.
9. THE HYPOTHETICAL PHYLOGENY OF THE PAUSSIDAE
(Plate IV)
I have already in a previous article l dealt with the family
of the Paussidae at considerable length. I arrived at the
conclusion that it was impossible for this family of beetles to
have been developed according to the Darwinian theory, but
at the same time I showed that, nevertheless, we must assume
a hypothetical evolution of the Paussidae, based ultimately
upon interior laws of evolution, but directed by exterior cir-
cumstances necessitating adaptation, and leading to the
production of the various genera and species of Paussidae
belonging to the Tertiary period, and thence, by a continuation
of the same process of evolution, to the production of the
present genera and species of the same family. Here again
the theory of permanence proves useless, whilst the theory of
evolution supplies us with a natural explanation of the origin
of those characteristics due to adaptation, which have made
the Paussidae genuine ant-inquilines.
Let us once more shortly review the phenomena in question.
(See Plate IV, at the end of the book.) The Paussidae
are called ant-beetles because they live in ants' nests ; the
most important feature characterising them as a family
is the great development of their antennae. They are found
all over the world, and we are acquainted with thirteen
living and three fossil genera (two of the latter being
identical with still existing genera) and almost three hundred
species.2
1 Stimmen aus Maria-Laach, LIII, 1897, pp. 400, &c. and pp. 520, &c.
2 Cf. R. Gcstro, ' Catalogo sistematico del Paussidi ' (Annali d. Museo
Civico d. Genova, [2] XX, 1901, pp. 811-850). To this catalogue must be added
a number of new species from Africa and India, which I described in Notes
from the Leyden Museum, XXV, 1904, pp. 1-82 with 6 plates ('Neue Beitrage
PHYLOGENY OP THE PAUSSIDAE 365
The Carabidae are the nearest natural relatives of the
Paussidae. Such is the opinion expressed by Burmeister,
Kaffray, Ganglbauer and Escherich, and it is confirmed by
my own anatomical examination of Paussus cucullatus, as a
series of sections that I made of this beetle showed the ovaries
of Paussus to resemble those of all the other Adephaga in
possessing meroistic, polytrophic egg-tubes ; in other words,
egg-tubes in which chambers containing eggs and nutriment
are arranged alternately.
As the Paussidae live with ants, their evolution out of the
Carabidae type cannot have taken place until the family of
ants had assumed an important biological position, viz. in
the first half of the Tertiary period, for before that time the
natural conditions requisite for the evolution of ant-inquilines
did not exist.
All the peculiarities which distinguish the Paussidae from
other beetles, and especially from the Carabidae, prove to be
due to adaptation to a myrmecophile existence ; this accounts
for the development of their massive antennae with a diminished
number of joints, and also for the formation of various organs
of secretion, which enable the beetles to attract the ants and
to live as their guests.
As I explained in a previous article,1 we can distinguish
three, or rather four3 chief groups of Paussidae, classifying
them according to the number of joints in the antennae of the
various genera, and these chief groups represent as many
stages in the process of evolving a true guest-relationship
between the beetles and ants. That the Paussidae, like the
Carabidae, originally had antennae with eleven joints is
rendered very probable by the fact that the genus Protopaussus,
found in Burma and China, still has such antennae. Next in
order come the genera with ten joints, viz. Homopterus, Cera-
pterus, Arthropterus and Pleuropterus. According to Motschul-
sky's description, the fossil genus Paussoides, occurring in
amber from the Baltic, had antennae with seven joints ; 3 and
zur Kenntnis der Paussiden, mit biologischen, und phylogenetischen Bemerk-
ungen'). The latter work forms a supplement to the account given in this
chapter of the phylogeny of the Paussidae.
1 Stimmen aus Maria-Laach, LIII, 1897, Part 5, pp. 522, &c.
2 Four, if we reckon the genus Protopaussus as belonging to the genuine
Paussidae.
3 Cf. von Motschulsky, Etudes Entomologiques, V, 1856, p. 26 with plate,
366 MODEKN BIOLOGY
the genera Pentaplatarthrus, Ceratoderus, and Merismoderus
have six. The fourth group consists of the genera having
antennae with two joints, viz. Lebioderus, Paussomorphus,
Platyrhopalus, Paussus, and Hylotorus. Photographs of some
representatives of these groups will be found on Plate IV.
Fig. 1 represents Pleuropterus brevicornis, a new species from
German East Africa, having antennae with ten joints ; fig. 2
represents Peniaplatarthrus natalensis from Natal, having six
joints; fig. 3 Lebioderus Goryi from Java with two joints;1
fig. 4 shows Paussus howa, and fig. 6 dama, both from Mada-
gascar, and fig. 5 Paussus spiniceps, a new species from Sierra
Leone in West Africa.
Comparative morphology and biology both show that, as
a rule, Paussidae with fewer joints and more complicated
development of antennae within any one genus approximate
more closely to perfection as inquilines, for the development
of the exudatory organs increases proportionately in beetles
which are true inquilines, and culminates in the genus Paussus.
In this genus we find an enormous variety of extraordinary
formations of the antennae, and also a great development of
tufts of yellow hair, of reddish yellow down and bristles, and
of exudatory pores and hollows. These latter assist in the
secretion of a peculiar substance, which the ants greedily
lick off their guests' bodies,2 and which is the return made by
them for the hospitality that they receive.
My anatomical and histological investigations of Paussus
cuculatus^ showed the glandular tissue producing this aro-
matic secretion to be situated chiefly in the hollows of the
antennae, under the pores on the brow, under the exudatory
hollow of the prothorax, and under the tufts of yellow hair
at the extremity of the abdomen. In Paussus spiniceps (Plate
IV, fig. 5) the organs of exudation are still better developed,
fig. 6. It is possible that there were only five joints, and the illustration
almost seems to suggest this, as the first three joints together greatly resemble
the first joint in the antennae of Ceratoderus or Paussus, and the four others
form a thick club.
1 The specimen sent me had been pierced with a needle, hence the dark
round spot on the right wing-sheath in the photograph.
2 On this subject see K. Eseherich's observations in his work ' Zur Anatomie
und Biologie von Paussus turcicus' (Zoolog. Jdhrb. Abt. /. System, XII, 1898,
pp. 27-70, with Plate II).
3 ' Zur naheren Kenntnis des echten Gastverhaltnisses,' &c. (Biolog. Zen-
tralblatt, 1903), pp. 232-248.
PHYLOGENY OF THE PAUSSIDAE 367
as the hollow of the antennae is serrate at the edge and provided
with yellow hairs, and the hollow of the prothorax is filled with
rolls of yellow hairs along the sides ; the ring of long reddish
yellow hairs at the extremity of the abdomen is so conspicuous
in this species that we may be sure Paussus spiniceps is a
very sweet guest, warmly welcomed by his West African hosts.
Paussus howa (fig. 4) has no tufts of yellow hair, but to
compensate for their absence the shell-like hollow in the
antennae contains an abundance of sweet substance. In this
species the two exudatory pores on the brow and the clefts of
the prothorax can be seen very plainly. In Paussus dama
from Madagascar (fig. 6), not only is the hollow of the prothorax
filled with, yellow hairs, but the whole body and even the
antler-shaped antennae are covered with bristles facilitating
exudation, and there are large exudatory furrows on the head.
In many other kinds of Paussus, especially in Paussus armatus
and its relatives, a hollow horn crowned with a tuft of yellow
hairs projects from the top of the head, and from it the ant
drinks its nectar, as once the heroes in Walhalla drank their
mead.
The position occupied by the genus Paussus among its
related genera cannot perhaps be better described, from the
standpoint of comparative morphology, than by a com-
parison that I have already used in this connexion.1 ' The
other genera of this family, which are very numerous, though
poor in species, resemble the various halting places in the
upward course of the evolution of the Paussidae. In the
genus Paussus an open plateau seems to have been reached,
offering abundant scope for the development of the most
varied kinds of ant-inquilines. This genus actually contains
more species than all the rest together (171 as compared with
118). Finally the genus Hylotorus, with its short, .almost
deformed antennae and legs, may be called a debased type,
displaying degeneration connected with excessive parasitism.
If we continue our simile, it represents a downward movement
from the height of the plateau on the further side of the
mountain.'
We now have to face the question : ' Is this evolution of
the Paussidae real or only imaginary ? Was each systematic
1 Stimmen aus Maria-Laach, LIII, 1897, Part 5, p. 524.
368 MODEKN BIOLOGY
species of this family created separately by God, as well in
the Tertiary period as in our own day ? Or are the genera and
species of the Paussidae the result of natural evolution of the
race, originating at the beginning of the Tertiary period with a
form like that of the Carabidae, and passing through various
stages of adaptation to a myrmecophile existence, until the
present multiplicity of forms was attained ? ' Whether we
consider the question from the point of view of philosophy
or of natural science, we shall, I think, have to accept the
latter theory, as it alone is capable of supplying a natural
explanation of the phenomena we have observed.
Of course there is no direct evidence that such an evolution
has taken place ; we cannot prove that at the present day,
from a beetle having ten joints in its antennae, one with six
joints may be evolved, nor that one with only two joints may
be descended from one with six. But if we are asked whether,
in course of the hypothetical phylogeny of the Paussidae, a
diminution in the number of joints in the antennae may not
have been produced in many genera by the joints growing
together in pairs or groups — this is quite another matter, and
this question must be answered in the affirmative.1
Let us consider the shape of the antennae in Lebioderus Goryi
(Plate IV, fig. 3). Most of my readers would say that there were
six joints in this beetle's antennae, but they would be wrong,
for the last five joints have grown together so as to form
one, although the original divisions between the joints are
still marked by deep depressions. We have, therefore, here
an unmistakable example of the manner in which a two-jointed
form of antennae can be produced from a six-jointed form by
the end joints growing together. Of course God could create
a Lebioderus, having the second joint of its antennae looking
exactly as if it were the result of five distinct joints having
grown together, but it savours too much of occasionalism for
me to be able to adopt this view, and I prefer the phylogenetic
explanation, according to which the club at the end of the an-
tennae in Lebioderus has really been formed by the coalescence
of five joints.
1 Escherich is mistaken when he asserts (Zoolog. Zentralblatt, 1899, No. 1,
p. 9) that I ever questioned this possibility. I only maintained that at the
present day it is no longer possible actually to observe such a reduction in the
number of joints.
PHYLOGENY OF THE PAUSSIDAE 369
In the present state of our knowledge we can hardly ex-
pect exact details regarding the hypothetical phylogeny of the
Paussidae ; we can hope to discover them only after both the
living and the extinct members of this family have been
studied with some approach to completeness. Hitherto only
scanty remains of three varieties of fossil Paussidae are known
to us from Baltic amber.1 These may be referred to the three
genera Arthropterus, Paussoides, and Paussus ; thus we already
have fossil representatives of three chief groups among our
present Paussidae, viz. those with ten-jointed antennae, those
with six (occasionally seven or five), and those with two. We
are therefore justified in concluding that, even in the middle
of the Tertiary period, the family of Paussidae was well
developed, at least in its principal groups.
Fossil Paussidae having antennae with eleven joints, ana-
logous to the present genus Protopaussus, have not yet been
discovered, but this is not surprising, as only two very rare
species of the living representatives of this genus are known to
exist. We know nothing with certainty regarding the previous
history of the Tertiary Paussidae, and can only suppose that they
are phylogenetically connected with the Carabidae of the Lias or
earliest Jurassic epoch. Taking into consideration the fossil
remains of Paussidae from the Miocene epoch, we must further
regard it as probable that the unknown hypothetical primitive
form of the Paussidae divided into the present four chief groups
in the first half of the Tertiary period, acting partly under
the influence of internal differentiation, and partly under that
of adaptation to a myrmecophile existence ; these four chief
groups being the Protopaussus group with eleven joints in the
antennae, the Arthropterus group with ten,2 the Paussoides
group with five or six, and the Paussus group with two.
The hypothetical phylogeny of the Paussidae took the
form probably of a tree with four chief stems, splitting up into
many smaller branches and twigs. The Paussidae of the
1 See von Motschulsky, Etudes Entomologiques, V, 1856, p. 26 ; C. Schaufuss,
' Preussens Bernsteinkafer ' I (Berl. Entomolog. Zeitechrift, XXXVI, 1891,
pp. 53 and 64) and II (ibid. XLI, pp. 51-54). The ants and Paussidae of the
Baltic amber do not belong to the Miocene, as was formerly believed, but to
the older Oligocene epoch. Cf. Handlirsch, Die fossilen Insekten, Leipzig,
1906-1908.
2 I have designated the groups according to the names of the oldest genus
in each.
2 B
370 MODEEN BIOLOGY
Tertiary period show that the four chief stems have followed
each an independent line of evolution, not standing in any
close relationship with the branches of other stems. Therefore
the present Paussus is not directly descended from the present
Lebioderus, nor is Lebioderus descended from the present
Arfhropterus or Homopterus, and least of all is Arfhropterus
descended from Protopaussus. The four great stems differ
greatly in the number of their branches and twigs. On the
lowest, the Protopaussus stem, we find only one genus with two
species ; on the Arthropterus stem, four genera with about
eighty species ; and on the highest, the Paussus stem, five
genera with over two hundred species.
By asserting that the chief stems of the Paussidae trunk
have continued an independent evolution ever since the early
part of the Tertiary period, I do not mean to deny the existence
of a remote connexion between the chief stems. The genus
Lebioderus, with its apparently six-jointed, but really two-
jointed antennae, is an interesting example of a ' collective
type,' marking the transition from genera with six-jointed
antennae to those with two ; but the actual time of the
transition is to be sought not in the Quaternary period at all,
but probably before the middle of the Tertiary.
Each of the four chief stems of the Paussidae trunk has its
own hypothetical phylogeny, and this has been influenced in
various ways by different internal tendencies and by different
degrees of adaptation to a myrmecophile existence. A few
examples will show what I mean.
Like the Carabidae, the genus Protopaussus has eleven joints
in its antennae, and the thickening of the joints is very slight
in comparison with the other Paussidae. On the other hand,
the broad, deep cavity of the prothorax and the yellow tufts
at the extremity of the abdomen show unmistakably that
this genus occupies a relatively high position as a genuine
inquiline. We have to distinguish the characteristics due to
organisation from those due to adaptation ; the retention of
eleven joints in the antennae is a characteristic due to organi-
sation inherited from the Carabidae, but the peculiar formation
of the prothorax and its means of secretion are due to adaptation,
and are characteristics acquired by this genus. The genera
with ten-jointed antennae are very different. Homopterus
PHYLOGENY OF THE PAUSSIDAE 371
and Arthropterus have enormously broad antennae, and their
massive shape and the diminution in the number of their joints
both are due to adaptation to the myrmecophile existence,
although they do not mark out these genera as true inquilines,
but, like the often very considerable thickening of the legs in
these creatures, suggest rather the offensive type, as these
peculiarities would serve to protect the beetles from being
attacked by the ants.1
Unmistakable evidence of adaptation to the position
of true inquilines is given first in this group by the genus
Pleuropterus (Plate IV, fig. 1), in which the pro thorax shows
a shell-like cavity, and becomes a large uneven exudatory
hollow, provided as a rule with yellow hairs, and at the same
time traces of yellow exudatory bristles appear more plainly
on the antennae. Within the Paussoides group, with antennae
having five or six joints, we meet with similar signs of inde-
pendent differentiation in various directions. The genus
Pentaplatarthrus (Plate IV, fig. 2) has developed in a manner
wholly unlike the genera Merismoderus and Ceratoderus. In
it the prothorax appears as an extraordinary labyrinth of
exudatory cavities and protuberances, pointing to a high
degree of adaptation to the position of inquiline, whilst the
long, flat antennae suggest the Arthropterus type.
In Merismoderus and Ceratoderus, on the other hand, the
prothorax is only slightly modified, but in the formation of
their antennae and in other points these two genera approach
the Paussus type. Among the genera having antennae with
two joints, Lebioderus (Plate IV, fig. 3) and Platyrhopalus stand
fairly close together ; to each belong a number of species
bearing a certain resemblance to the genus Paussus, yet not so
great a resemblance as to justify our believing this genus to be
directly connected with the other two. Hylotorus is likewise
very closely related to Paussus. Within the genus Paussus
the evolution of the same generic type proceeds along two lines,
and we find a series of species having the prothorax undivided,
and others in which a deep cleft divides the prothorax into
two parts, between which is situated the large exudatory cavity
of the thorax.3 The latter branch in particular splits up into
1 Cf. Stimmen aus Maria-Laach, LIII, 1897, Part 5, pp. 521, 522.
2 The species depicted on Plate IV, figs. 4-6, belong to the second group.
2 B 2
372 MODEKN BIOLOGY
a number of smaller branches, representing a considerable
number of systematic species, that stand in close relation-
ship to one another. The different species display an
immense variety in the shape of the second joint of the
antennae and in the development of the yellow hairs and
other organs of secretion ; I shall refer to these points again
later on.
One more remark must be made with reference to the
hypothetical phylogeny of the Paussidae.
The above account suggests that it is monophyletic in
character, originating in one single pre-Tertiary primitive
form. But the genus Protopaussus, which I have designated
the oldest stem of the one trunk, and nearest to the original
(although its existence in the middle of the Tertiary period
has not been proved), may possibly have had an independent
origin, and be descended from a kind of Carabidae differing
from the ancestors of the other three chief groups of
Paussidae. Its origin may be of more recent date than
that of the other groups which existed even in the
Miocene epoch. This supposition would explain why the
antennae of Protopaussus resemble those of the Carabidae more
closely than those of the genuine Paussidae. If this view is
correct, the evolution of the family of Paussidae is not mono-
phyletic but diphyletic. The two lines of descent have been
quite independent of one another ; one originated in a pre-
Tertiary form of Carabidae, and early in the Tertiary period
produced the genera Arthropterus, Paussoides and Paussus ;
the other originated later, perhaps in the second half of the
Tertiary period, from another kind of Carabidae, and produced
only the present genus Protopaussus.
It is not possible as yet to say with certainty which of these
two suppositions is more correct, whether we are to believe
the evolution of the present Paussidae to have been mono-
phyletic or diphyletic ; perhaps future palaeontological dis-
coveries will settle the matter.
I have discussed the evolution of the Paussidae in detail,
because it may be useful in correcting some false impressions,
which prevail in many quarters, regarding the relationship
existing between genera and species of the same family. It
removes also many difficulties raised against phylogenetic
EVOLUTION OF THE PAUSSIDAE 373
hypotheses by those who have not made a special study of the
subject.
Respecting the causes of the hypothetical evolution of the
Paussidae, we have to content ourselves with a few suggestions,
as we know very little about them. Undoubtedly the interior
capacity for modification, possessed by the primitive form, must
be regarded as the first and most indispensable cause of the
evolution of the Paussidae ; otherwise their adaptation to a
myrmecophile existence would have been impossible, and
still less would there have been any possibility of an adaptation
so varied and so complete as to transform the whole bodily
structure of these beetles that were once Carabidae, to reduce
the number of joints in their antennae, whilst rendering them
thick and massive, and to equip them with very various organs
of exudation and the corresponding tissues.1
The evolution of the Paussidae was probably neither so slow
nor so gradual a process as the Darwinian hypothesis would
require it to have been ; it is likely that in many cases the
changes were effected suddenly, and were such as the theory of
mutation assumes to have occurred. This is suggested not only
by the fact that many genera of Paussidae at the present day
are separated from one another by wide intervals, but also by
the circumstance that the three chief groups of this family are
represented among the fossils of the Tertiary period. That a per
saltum modification was probably possible in this case — such a
modification as a growing together of definite pairs of joints
in the antennae — is seen in Lebioderus Goryi (Plate IV, fig. 3),
which, with regard to the formation of its antennae, stands
on the border line between the six-jointed and the two-jointed
forms. The absence of transitional links between many genera
and species of Paussidae can be accounted for more easily,
if we believe the progressive modifications to have been
effected per saltum, than if we assume the process of change to
have been extremely gradual. A very gradual change may
have taken place within some groups in the case of very
closely allied species, e.g. the species of the group Paussus
denticulatus Westw., but it is hardly possible to see how such
1 The latter are adipose glandular tissues and are, strictly speaking, meta-
morphosed hypodermic cells. Cf. 'Zur naheren Kenntnis des echten Gast-
verhaltnisses,' &c. (Biolog. Zentralblatt, 1903), pp. 68, 232, &c.
374 MODEKN BIOLOGY
a gradual process could have resulted in the production of the
chief genera of Paussidae.
Of course, in considering the hypothetical evolution of the
Paussidae, we must ascribe great importance to the exterior
as well as the interior factors of evolution, for all the morpho-
logical peculiarities that distinguish the Paussidae from their
nearest relatives, the Carabidae, are due to their adaptation
to a myrmecophile existence. The unusual breadth of the
antennae and the diminution in the number of their joints are
characteristics due to adaptation,1 as is the wonderful variety
in the shape of the antennae in the genus Paussus, each tending
to make the flagellum firm and convenient for the ants to seize
with their jaws, and use as a means of picking up their guests
and carrying them about, whilst at the same time in most cases
each modification makes the flagellum a more perfect organ of
exudation, whence the ants can lick their favourite dainty.3
Other characteristics due to adaptation are the different
kinds of hair connected with the secretion of this substance ;
there are tufts of yellow hairs, downy hairs of a reddish yellow
colour, bristles, &c., situated on various parts of the bodies
of these true inquilines, on the antennae, on the horn, in
the cavity of the prothorax and at its edges, at the edges of
the wing-sheaths or on their surface, at the extremity of the
abdomen, and even on the legs. Other marks of adaptation are
the manifold exudatory pores, the horns on the head, and
the cavities and furrows on the prothorax. Others again are
the peculiar exudatory tissues, which are connected with the
external organs of secretion, and, as adipose glandular tissue,
approximate partly to the adipose tissue and partly to the
common glands of the skin, and furnish the aromatic secretion
of which the ants are so fond, that in order to obtain it they
keep the beetles in their nests. We may therefore say :
'Adaptation to a myrmecophile existence, and especially
adaptation to various degrees in the progressive evolution of
true inquilines, is the leading idea governing the evolution of
the whole family of Paussidae.1 But at the same time we must
1 Cf. on this subject Stimmen aus Maria-Laach, LIU, 1897, Part 5, pp. 521,&c.
2 Cf. Stimmen aus Maria-Laach, LIU, 1897, Part 5, pp. 525-528, and * Zur
naberen Kenntnis des ecbten Gastverhaltnisses ' (Biolog. Zentralblatt, 1903),
pp. 242-248.
EVOLUTION OF THE PAUSSIDAE 375
acknowledge our present inability to explain how this idea
has been carried out in the individual cases ; how exterior
causes, such as the hospitality shown by the ants and natural
selection, have co-operated with the interior factors that
produce tissues and organs, so as to effect adaptation so varied
in form and of so high a degree of completeness.
Let us turn our attention to one of the most interesting
phylogenetic problems, viz. to the differentiation in the shape
of the antennae within the genus Paussus, which contains
almost two hundred species (cf. Plate IV, figs. 4-6). To what
natural causes can we ascribe the extraordinary variety in the
shape of the flagellum in this genus ? It is at first sight an un-
accountable freak of nature ; and it seems as if some skilful
artist must have produced almost every conceivable shape,
working quite arbitrarily and without any definite purpose ;
fashioning the flagellum now in the shape of a lens, now like
a ball, a club, a sabre, a triangle, a leaf, a rod, a horn, a shell,
an antler, adorned with all manner of zig-zags, furrows and
points, each being a miniature work of art, given by the
Creator to be the plaything of the ants, His favourites in
the insect world.
If we study the biology of the Paussidae, we shall soon
come to the conclusion that these various shapes of the
antennae in the genus Paussus are by no means useless play-
things, but are all different solutions of the phylogenetic
problem, ' How can the nose of a beetle (for the antennae are
primarily organs of smell, or movable noses) be at once bene-
ficially and pleasantly applied to another biological purpose ? ' l
Or the question may be worded more precisely thus :
' How can the nose of an ant-inquiline be changed into a
means of transport, by which the ants can seize their guest
with their jaws and carry him away without injuring him ? and,
further, how can the nose at the same time be made into an
organ for exudation, whence the ants derive their delicious
nectar ? ' In other words : the object aimed at in the
characteristic metamorphosis of the flagellum of the Paussus
antennae is fitness to discharge two biological functions, to
be at the same time means of transport and of exudation ;
1 Cf. Stimmen aus Maria-Laach, XL, 1891, pp. 79, 207, 320, 406, &o., also
LI1I, 1897, pp. 520, &c.
376 MODEEN BIOLOGY
and the Paussus antennae fulfil these two requirements with
greater perfection, the higher the stage of genuine guest-
relationship attained by their owner.
The species with lens-shaped antennae are those members
of this genus which have retained the simplest form, nearest
to the original, and they have as a rule their exudatory organs
only slightly developed. Antennae shaped like rods, sabres,
or antlers belong to species in which the guest-relationship
is at a higher stage, and it is highest in those in which the
flagellum is hollowed out, so as to form a cup to contain the
secretion, especially if, as in Paussus spiniceps (Plate IV,
fig. 5), this cup is surrounded by notches bearing tufts of
long, yellow hair.
It is possible therefore to discover both a biological and
a phylogenetic explanation of the idea controlling the morpho-
logical variety of form in the Paussus antennae. It cannot be
denied that natural selection at first sight seems likely to
have encouraged this variety, as it might select such antennae
as best fulfilled the above-mentioned biological requirements
— these antennae being the result of the action of the interior
laws of evolution belonging to the various species. Closer
examination, however, shows that Darwin's natural selection
cannot give a satisfactory account of the actual specific
multiplicity of shape in the antennae of Paussus.
If natural selection were the controlling factor in the
specific evolution of the antennae within the genus Paussus,
their form would have to originate in accordance with a strict
necessity for adaptation, which would eliminate antennae
of other shapes as less capable of existence, for this is precisely
what is implied by the ' Survival of the Fittest in the Struggle
for Existence.' Consequently natural selection would lead
to the production of one definite form of Paussus, having
antennae of one fixed shape, and living with one particular
species of guest-ant. The shape of the antennae would be
determined by the mechanical necessity for their adaptation
to the shape and size of the ant's head, the length and breadth
of its upper jaw, and its manner of seizing the beetle, carrying
it and licking it. Moreover, the varieties of Paussus, living
with allied species of the same genus of ants, could differ
from one another only as far as was absolutely necessary to
ANTENNAE OF THE PAUSSIDAE 377
adapt' them to various species of hosts ; for otherwise they
would perish in the struggle for existence, as being less capable
of life. Let us see how the actual facts stand in relation
to the Darwinian hypothesis. They simply do not tally with
it at all ; about two-thirds of the almost two hundred species
of Paussus hitherto discovered live exclusively with ants of
the genus Pheidole, the workers and warriors of which genus
resemble one another very closely even in different species ;
and yet in the Pheidole nests occur species of Paussus with
antennae of all the above-mentioned shapes, except perhaps
those with long antler-like antennae, which probably have
larger ants as their hosts. Moreover, within the genus Pheidole
there are a good many species which entertain a considerable
number of kinds of Paussus, having antennae of very various
shapes. For an instance I may refer to Pheidole megacephala
in South Africa, which has over a dozen species of Paussus
as inquilines, and of these, according to observations made
by Dr. Hans Brauns and G. D. Haviland, nine live with
Pheidole megacephala var. punctulata. Among them are,
according to the species in my collection, Paussus Klugi and
Curtisi with rod-like antennae, Paussus cultratus and granulatus
with the flagellum shaped like a knife, and Paussus cucullatus
and Elisabethae, in which it is shaped like a shell.
There are at least five species of Paussus with antennae
of different shapes living with Pheidole latinoda in India, and
as many with Pheidole plagiaria in Java.
I believe therefore that Darwin's theory of natural selection
cannot give a satisfactory explanation of the specific differentia-
tion of the antennae in various species of Paussus. On the
contrary, the multiplicity of their shapes gives us an impression
that the phylogenetic evolution of the antennae in Paussus
has freed itself to a great extent from the strict laws of natural
selection, which would tend to produce uniformity, and not
multiplicity of shape.
But how can the great variety of extraordinary shapes
have been produced by natural methods within the genus ?
Primarily as a result of the action of the interior laws of growth,
which involved a particularly high degree of variability in
the flagellum of the antennae.
The hypothetical previous history of the genus Paussus
378 MODEEN BIOLOGY
suggests a reason why the flagellum in this genus tends to
develop into so many different shapes. The present flagellum
with a single joint was not originally so simple, but has been
produced by a number of original joints growing together ;
the tendency to vary in shape, displayed by the flagellum
of Paussus, is due to the combined tendencies to vary, possessed
by its original components.
Let us refer once more to Plate IV, fig. 3, and look closely
at the antennae of Lebioderus Goryi. The flagellum has one
joint, but there is no difficulty in seeing that it consists of
five separate joints grown together, and these apparently
separate joints are formed from nine or ten original joints,
that have grown together in pairs.1
In a great many kinds of Paussus with a highly developed
rod or shell-shaped flagellum, there is a row of seven or eight
transverse furrows on the back of the flagellum and inside
the cavity of the antennae, the furrows being separated by
teeth or notches at the edge. (See Paussus howa, Plate IV,
fig. 4.) The antler-shaped flagellum of Paussus dama shows
a similar peculiarity (fig. 6). The teeth or notches on the
flagellum, separated by transverse furrows, are probably
traces of original segmentation.
I have, I think, said enough to prove that the flagellum
of Paussus is rendered capable of development into many
different shapes by certain interior causes. In order to fix
this tendency to vary, and limit it to the production of definite
forms, another factor is required, which must be exterior.
As I have already shown, natural selection can act only in a
very restricted manner ; in fact, it would be more likely to
hinder than to promote the development of the great variety
of forms that actually exist. How are we therefore to account
for the specific differentiation of the antennae in the genus
Paussus ? A comparison that I have used on a previous
occasion2 may serve to elucidate my view of the matter.
1 I cannot decide whether the ten- join ted antennae of Arthropterus, Cera-
pterus, and Pleuropterus (Plate IV, fig. 1), in which the flagellum consists of
nine joints, have been formed from eleven-jointed antennae by the reduction
of the second joint to a small connecting link between the scape and the
flagellum, or by the amalgamation of the two last joints of the flagellum.
Reasons can be adduced in support of both these views.
2 ' Zur Entwicklung der Instinkte,' pp. 182, &c. (Verhandl d. Jc. k. Zoolog.
Botan. Gesellschaft, Vienna, 1897, Part 3, pp. 168-183).
TEKMITOXENKDAE 379
Man is able, by means of conscious selection, to produce
a great variety of breeds among the domestic animals ; for
instance, he has bred pigeons differing in plumage, in the
formation of the crop, tail, &c. In exactly the same way,
though unconsciously, the ants have bred inquilines of the
genus Paussus with antennae of very various shapes. If certain
shapes found favour with the ants, this was enough to give
an impetus to a further evolution in that direction, for guests
with antennae of the attractive shape received better treatment
from their hosts than others. In this way varieties of Paussus,
differing in the shape of their antennae, might develop in the
nests of one and the same species of ant. The beetle's capacity
for existence was not affected by its having a flagellum of one
shape rather than another, hence the struggle for existence
cannot be made responsible for the selection of any particular
shape. I have designated the instinctive selection practised
by the ants in breeding their genuine inquilines ' Amical
Selection,' as. opposed to Darwin's ' Natural Selection.' l
We met with this new form of selection in discussing the
hypothetical phylogeny of the Lomechusini (p. 338), and
here again, in the case of the Paussidae, we are induced to
accept it, as it is based upon very simple and obvious con-
siderations. If, however, there is anyone to whom it does
not commend itself, he is perfectly free to devise a better
explanation.
10. THE TERMITOXENIIDAE, A FAMILY OF DIPTERA
(See Plate V)
In the nests of African and Indian termites are found
some remarkable Diptera belonging to the family of Termito-
xeniidae.1*
1 Biolog. Zentralblatt, 1901, No. 23, p. 739, &c., Escherich's objections, which
appeared in the same paper in 1902, p. 658, were answered in it in 1903, p. 308.
I need scarcely say that I do not ascribe to the ants any ' aesthetic sense of
shape.' The kind* of instinctive selection, practised by the ants in their dealings
with the Paussidae, depends chiefly upon their sense of touch, but also upon
taste and smell, and only incidentally upon sight.
2 Cf. Wasmann, ' Termitoxenia, ein neues fliigelloses physogastres Dipteren-
genus aus Termitennestern,' I and II (Zeitschrift fur wissenschaftl. Zoologie
LXVII, 1900, Part 4, and LXX, 1901, Part 2) ; ' Zur naheren Kenntnis der
termitophilen Dipterengattung Termitoxenia ' ( Verhandl. des V internationalen
380 MODEKN BIOLOGY
They have been mentioned in previous chapters, and
photographs of them will be found on Plate V, figs. 1-6. They
form the genus Termitoxenia Wasm. and its subgenus Termito-
myia Wasm. These little creatures, only 1-2 mm. in length,
are white or pale yellow in colour, and are some of the most
remarkable insects in existence. They have neither males nor
females like other insects ; they do not go through a larval
stage nor have they wings like other Diptera. They are
protandric hermaphrodites ; a stenogastric imago form takes
the place of the larval stage, and very remarkable appendages
on the thorax represent wings. In one of the two subgenera,
i.e. in Termitoxenia in the narrower sense, the whole embryonic
development seems to take place in the parent, so that the
stenogastric imago form is born alive.1
The stenogastric imago (Plate V, figs. 1 and 2) is, however,
a walking embryo, for its abdomen especially resembles that
of a larva, and the fat-body and the muscular system exist
in a very rudimentary form ; in very young specimens of
Termitoxenia Assmuthi I have found even the vitelline sac
of the embryo. It is only after the stenogastric imago has
seen the light that it undergoes an ' imaginal development/
which takes the place of the usual larval development, and
thus it gradually reaches the physogastric imago form, repre-
senting the full-grown insect (Plate V, figs. 3 and 6). In
each individual the male generative glands ripen first, and
the ovaries later ; hence we have here an instance of protandric
hermaphroditism. The development of the ovaries is accom-
panied by a steady increase in physogastry, until finally the
adult insect resembles a whitish sac attached to the forepart
of the body as to a small, black stalk. In spite of the unwieldy
size of their bodies, their long, powerful legs enable these
Zoologenkongresses zu Berlin, 1901, Jena, 1902, pp. 852-872 with plate) ;
* Termiten, Termitophilen und Myrmekophilen, gesammelt auf Ceylon von Dr.
W. Horn ' (Zoolog. Jahrbiicher, AU. fur Systematik, XVII, 1902, Part 1, pp.
151-153 with Plate V, figs. 4, 4 a-c, and 5) ; ' Die Thorakalanhange der Ter-
mitoxeniidae, ihr Bau, ihre imaginale Entwicklung und phylogenetische
Bedeutung ' (Verhandl. der Deutschen Zoolog. Gesellschaft, 1903, pp. 113-120 with
Plates II and III) ; * Neue Termitophilen aus dem Sudan ' (Results of the
Swedish Zoological Expedition to Egypt and the White Nile, 1901, under the
direction of L. A. Jdgerskiold, No. 13, Upsala, 1904) ; see also remarks on
Termitoxenia in the present work, Chapter II, p. 38, and Chapter III, p. 50.
1 This statement is borne out by a series of sections made of a specimen
of T. Braunsi, containing an embryo.
TEKMITOXENIIDAE 381
creatures to run quickly, as Father Assmuth observed, when
he was studying Termitoxenia Assmuthi. In the Termitoxeniidae
the place of the wings in other Diptera is taken by a pair of
oar- or hook-shaped appendages on the mesothorax (Plate
V, ap in figs. 1, 2, 4, 5), which serve a number of important
biological functions, but do not enable the creatures to fly.
They act as balancing poles, and maintain the fly's equilibrium
when it runs ; they are means of transport, by which the
delicate little guests can be picked up by their hosts without
injury ; they are also important sense-organs, for the front
branch of each thoracic appendage contains a large nerve,
and is covered with tactile bristles ; they are finally the
chief organs of exudation possessed by these genuine inquilines,
for the hinder branch of each appendage is a hollow tube,
at the upper end of which is a cluster of large membranous
pores (Plate V, pp in figs. 4 and 5). As is generally the
case in physogastric inquilines among termites, the exudation
which is eagerly licked off by their hosts, and which secures the
inquilines their position as favoured guests, is a constituent of
the blood-plasm.1
Behind these appendages of the mesothorax, which answer
to the front wings of other Diptera, there is on the metathorax
a pair of very diminutive balancers, of very primitive structure,
which are essentially equivalent to the genuine halteres of
the Diptera.
Let us now consider these interesting creatures from the
point of view of the evolution theory. What right have we
to assign a place in the Diptera order to them, as they have
no wings ? Moreover, Termitoxenia has an incomplete metamor-
phosis, and Termitomyia has none at all, whereas a true larval
form always occurs in other Diptera, even in those that give
birth to living pupae ; but here, in place of the larva, we have
a stenogastric imago. The protandric hermaphroditism of
these diminutive beings is a characteristic that does not present
itself regularly in any other insect. From the standpoint of
the theory of permanence we must say: The Termitoxeniidae
are a class apart, resembling real Diptera in many respects,
such as in the shape of their antennae, in the formation of their
1 Cf. ' Zur naheren Kenntnis des echten Gast verbal tnisses ' (Biolog.
Zentrattlatt, 1903), pp. 68, 300, 305.
382 MODEBN BIOLOGY
proboscis (which is used to suck the life out of the young
termites), and in having halteres instead of hind wings. But
these resemblances are insignificant in comparison with the
great differences mentioned above, which distinguish them
from Diptera. If therefore the Termitoxeniidae were created
once for all in their present condition, they ought to be classed
as an order of insects resembling Diptera, but not belonging
to them.
From the standpoint of the evolution theory we should say :
These curious creatures were once genuine Diptera, and all
their divergencies from the normal type of that order are due
to adaptation to a termitophile existence. The peculiar
appendages to the mesothorax (Plate V, ap in figs. 1, 2, 4, and
5) are the result of metamorphosis of the front wings which
their ancestors once possessed ; for these appendages were
better adapted than wings to the changed conditions of life
within the nests of the termites. As the development of the
individual was shortened, the larval stage, that the creature's
ancestors had passed through, was omitted and replaced by the
stenogastric imago form, and in the subgenus Termitomyia
the process is still more abbreviated, and the stenogastric
imago form does not enter the world as an egg but as a living
creature.
This abbreviation and simplification of the development of
the individuals belonging to this genus is phylogenetically to
be referred to the fact that the conditions for nourishing them-
selves and their young were very favourable in the termite
nests. It is a general rule that the number of eggs in an insect
stands in inverted ratio to the number of eggs and larvae
that develop successfully : the less favourable the external
circumstances, the greater the number of eggs laid by an insect
to assure the propagation of its species ; and the more favour-
able the conditions, the fewer the eggs. Hence the number of
eggs was very small in the case of the Termitoxeniidae, and
consequently each egg-cell could be supplied with a greater
abundance of nourishment (cf. Plate V, fig. 6 ov). The
result of this was a quickening of the development of the
individual, and an abbreviation and simplification of the
cycle of reproduction. This explains why in Termitoxenia
the larval stage fell out and was replaced by the stenogastric
EVOLUTION OP TEEMITOXENIA 383
imago form, and also why in the subgenus Termitomyia the
imago form does not proceed from the egg, but appears at once
alive. All this is only a consistent continuation of the abbre-
viation and simplification of the individual development.
The hermaphroditism of Termitoxenia is a phenomenon that
appeared later in the phylogeny of these little Diptera. As
they live inside the termite nests, no crossing could occur
between the occupants of different nests, when once their
wings had suffered metamorphosis, and served other biological
purposes than that of flight. When they became able to
dispense with the advantages of crossing, the distinction of
the sexes gradually ceased, for its chief object is to cause union
between individuals differing as widely as possible within the
species. Under similar circumstances among other insects
parthenogenesis has taken the place of sexual propagation,
but Termitoxenia developed hermaphroditism, which is to
some extent a still more advanced simplification of the method
of propagating the species.
Thus we see that the theory of evolution really enables us
to understand how the Termitoxeniidae have phylogenetically
been evolved out of ordinary insects with two wings, and at
the same time this theory suggests why we may rightly class
them with the Diptera. Certain morphological points of
agreement between the Termitoxeniidae and the Muscidae
on the one hand, and the Phoridae on the other, lead us to
regard the Termitoxeniidae as a branch of the Diptera stock,
connected originally with the Muscidae and Phoridae, but
having adopted a line of evolution peculiar to itself, in conse-
quence of its thorough adaptation to the termitophile existence.
Many points in this explanation may still appear very
doubtful, but it must be granted that it supplies us with a real,
scientific means of accounting for the morphological and
embryological peculiarities of Termitoxenia, which stand in
very close connexion with its biology. Unless we assume
that these creatures are of common origin with true flies, we
are not justified in including them among the Diptera ; we
should be forced to say with the theory of permanence : ' These
creatures are entia sui generis, created in their present form
to be the inquilines of certain species of termites, which were
likewise created exactly as we see them.' In this way an
384 MODEEN BIOLOGY
apparently satisfactory account is given of the facts before us,
inasmuch as they are referred to the Creator's wisdom and
power as their immediate cause. Nevertheless, I prefer the
other interpretation, which refers to the Creator's wisdom
and power only indirectly, and seeks to discover the natural
causes, through which God in His wisdom and power has
produced these beneficial adaptations by means of phylo-
genetic evolution, for this hypothesis is based upon a logical
application of the fundamental principle : * God does not
interfere directly in the natural order when He can make use
of natural causes, and the natural laws laid down by Him are
already in force.'
There is one point in the ontogeny of Termitoxenia that
we must discuss shortly, as it is of particular importance to the
phylogenetic account of these inquilines, viz. the development
of the appendages on the mesothorax, that take the place of
wings. In Termitoxenia mirabilis Wasm. of Natal (cf. Plate V,
fig. 2, ap), which belongs to the subgenus Termitomyia, these
appendages are shaped like hooks, and consist of two tubes
resembling tracheae, and only partially grown together. This
formation, which somewhat resembles the breathing tubes of
insect larvae living in water, remains unchanged from the
earliest stenogastric to the latest physogastric imago form.
The tissues contained in these tubes also are unchanged
throughout the whole period of imaginal growth ; the front
branch is always an organ of touch and contains a nerve, the
back branch is connected with the circulation of the blood and
with exudation. In the sub-genus Termitoxenia, howrever, in
T. Havilandi of Natal, T. JagersUoldi of the White Nile, T.
Heimi and Assmuthi of the East Indies, the original tubes
grow more closely together, and in the earliest stenogastric
imago (cf. Plate V, fig. 1, ap) they might almost be taken
for small, stunted wings, but later on they gradually draw
together so as to form the oar- or style-shaped horns which are
seen in the adult physogastric animal (cf. the photograph,
greatly enlarged, on Plate V, figs. 4 and 5). In the stenogastric
individuals of the three species at present known of the sub-
genus Termitoxenia, these growths resemble one another very
closely, but they differ in the physogastric specimens according
to their species. In T. Heimi (Plate V, fig. 4), even in their
EVOLUTION OF TEKMITOXENIA 385
final form they bear more likeness to wings than they do in
the other Indian species, T. Assmuthi (fig. 5), in which they
gradually become like rods, and lose their early resemblance
to wings (fig. 1). It is very remarkable that one species found
in what used to be the Orange Free State, viz. Termitoxenia
(Termitomyia) Braunsi Wasm., is a perfect connecting link
between T. mirabilis and the other four species, as far as the
appendages on the thorax are concerned. Still more striking
is a discovery that I made when cutting under the microscope
a series of sections of a very young stenogastric specimen of
T. Heimi. I found the appendages to be at a stage of develop-
ment at which real wing-veins occur all round the hind branch,
but they are suddenly suppressed and are absent in slightly
older specimens.
What do we learn from these facts considered in their
bearing upon the theory of evolution ? They tell us that the
subgenus Termitomyia (mirabilis and Braunsi), which is vivi-
parous, departs furthest from the original Diptera type in
the formation of the appendages on the thorax, whilst the
subgenus Termitoxenia (Havilandi, Heimi, Assmuihi, and
Jdgerskioldi), which is oviparous, stands nearer to the genuine
Diptera in this respect. This enables us to understand why in
the latter subgenus, at a particular point in its ontogeny,
there is a genuine but transitory atavism, during which the
ancestral wing-veins appear, as if in memory of the past, and
then vanish. In other words : The tendency to produce real
wings, which in the ancestors of Termitoxenia continued without
interruption, is still present at the beginning of the ontogeny
of our Termitoxenia, but is suddenly broken off and diverted
to other channels, leading to the formation of appendages
on the thorax that are quite unlike wings. In the subgenus
Termitomyia, especially in T. mirabilis, the development of
these appendages proceeds uninterruptedly on the new lines, and
does not pass through a stage of resemblance to wings. This
subgenus dates from an earlier period and is further removed
from the Diptera type. This explanation, which the theory
of evolution supplies, seems to me the only scientific mode of
accounting for the facts, which are an inexplicable * freak,'
when considered with reference to the theory of permanence.
In order to study the anatomy, growth, and mode of life
2 o
386 MODEKN BIOLOGY
of these interesting little termite-inquilines, I have cut 10,000
microscopical sections from sixty specimens of five different
species of Termitoxeniidae, and from them I have obtained
much evidence in support of the theory of descent. Without
any exaggeration we may assert that this family of Diptera is
perfectly incomprehensible both morphologically and biologi-
cally, unless in studying it we take evolution into account.
It is almost impossible to dispense with the theory of descent, if
we attempt to give a reasonable explanation of the scientific facts.
No detailed argument is needed to show that the
hypothetical evolution of the Termitoxeniidae is not to be
understood in the Darwinian sense. The theory of selection
shows us the external reason why the better adapted forms
survived, whilst others less capable of existence died out, but
it cannot suggest any internal reason for the origin of these
beneficial modifications and their regular and progressive
development. If the Diptera ancestors of these curious
creatures had possessed no interior capacity for adaptation
to a new mode of existence, they could never have become
Termitoxeniidae, and the termites would never have enjoyed
the company of these pretty and interesting guests.
Unless we believe in the occurrence of variations with a
definite aim among the chromosomes of the germ-plasm, it is
simply impossible to explain the complete and thorough
changes in the whole organism, mode of propagation and
development, that take place in these tiny termitophile Diptera.
11. THE HISTORY OF SLAVERY AMONGST ANTS
Slavery is an ominous word when used in the history of
mankind ; it is a little word, but it conveys the idea of bound-
less injustice and cruelty, of misery and degradation. But
when used with reference to ants the meaning of the word is
different, and if we study the subject we gain an insight into
these creatures' wonderful instinct, and are filled, not with
horror and indignation, but with astonishment and admiration.
In the foregoing sections of this chapter I have reviewed
a number of beetles and flies, living as inquilines amongst ants,
and have shown that our present systematic species, genera,
and sometimes also families of these inquilines must be regarded
SLAVERY AMONGST ANTS 387
as the result of phylogenetic adaptation to the myrmecophile
or termitophile existence.
Let us now consider an example which ought to throw some
light upon the phylogenetic evolution of the instincts.
Previous articles published in Stimmen aus Maria-Laach l
have made my readers familiar with the fact that among
ants some are slave-holders, which steal the workers of
other species as pupae, carry them to their own nests, and there
bring them up to work for them. That the red robber-ant
(Formica sanguinea) and the red Amazon ant (Polyergus
rufescens) behave thus, has been known in Europe for the
last hundred years, ever since Peter Huber published his
classical studies ; and later observations have considerably
enlarged Huber's discoveries, and have extended them to the
American connexions of our robber-ants.2
1 ' Aus dem Leben einer Ameise ' (XXXI, 1886, 413-741) ; « Die Lebens-
beziehungen der Ameise ' (XXXVII, 1889).
2 The chief works on this subject are : Pierre Huber, Becker ches sur les
mozurs des fourmis indigenes, 1810, nouvelle edit., Geneva, 1861. J. Hagens,
' tiber Ameisen mit gemischten Kolonien ' (Berl Entomol. Zeitschr., XI, 1867,
101-108). Aug. Forel, Les fourmis de la Suisse, Bale, &c., 1874 ; * Etudes
myrmecologiques ; Miscellanea myrmecologiques,' I (Strongylognathus
Christophori), (Revue Suisse de Zoologie, XII (1904), 1-52) ; ' Sklaverei," Symbiose
und Schmarotzertum bei Ameisen ' (Mitteilungen der Schweiz. Entomol. Gesell-
schaft, XI, 1905, Part 2, 85-89) ; ' Miscellanea myrmecologiques,' II (Annales
de la Societe Entomologique de Belgique, XLIX, 1905, 191, &c.) (Wheeleria Sant-
schii) ; ' Moeurs des fourmis parasites des genres Wheeleria et Bothriomyrmex '
(Revue Suisse de Zoologie XIV, 1906, fasc. 1, 51-69). John Lubbock (Lord
Avebury), Ants, Bees and Wasps, London, 1904. H. C. McCook, ' The shining
slavemaker (Polyergus lucidus) ' (Proceed. Acad. Nat. Sci., Philadelphia, 1880,
376-384). Gottfr. Adlerz, Myrmecologiska studier, II, Stockholm, 1886, and
III, Stockholm, 1896. Ch. Janet, Conference sur les fourmis, Paris, 1906
(pp. 27-28 on Anergates) ; Rapports des animaux myrmecophiles avec les fourmis,
Limoges, 1897 (p. 57 on Anergates). M. Ruzsky, 'Neue Ameisen aus Kussland '
(Zoologische Jahrbucher Abt. fur Systematik, XVII, 1902, 469-484), (Myr-
moxenus) ; ' Die Ameisenfauna der Astrachanischen Kirghisensteppe ' (Horae
Societatis Entomologicae Rossicae, XXXVI, 1903, 1-25, published separately).
E. Wasmann, Die zusammengesetzten Nester und gemischten Kolonien der
Ameisen, Miinster, 1891 ; Vergleichende Studien iiber das Seelenleben der
Ameisen und der hoheren Tiere, Freiburg i. B., 1900 ; ' Neues iiber die zusam-
mengesetzen Nester und gemischten Kolonien der Ameisen ' (Allgemeine
Zeitschrift fur Entomologie, 1901, 1902) ; * Ursprung und Entwicklung der
Sklaverei bei den Ameisen' (Biolog. Zentralblatt, XXV. 1905, Parts 4-9,
Supplement in Part 19, pp. 644-653) ; ' Wie grunden die Ameisen neue
Kolonien ? ' (Paper read in the natural science section of the Gorresgesellschaft
at Bonn, on September 27, 1906, published in the Wissenschaftliche Beilage
to the Germania, No. 44, November 1). W. M. Wheeler, 'The compound and
mixed nests of American ants' (American Naturalist, XXXV, 1901, Nos. 414,
415, 417, 418) ; ' Three new genera of inquiline ants from Utah and Colorado '
(Bullet. American Museum of Nat. History, XX. 1904, 1-17) ; 'A new type of
social parasitism among ants ' (Bullet. American Museum of Natural History,
2 c 2
388 MODEKN BIOLOGY
Let us imagine that on a hot July afternoon we are standing
beside a little mound in the grass, containing a nest of Amazon
ants (Polyergus rufescens) with their slaves (Formica rufibarbis). l
A few minutes ago only reddish grey slaves 3 were running
busily about the entrances to the nests, occupied with making
earth-works, or were coming home laden with honey after a
visit to the aphides, or were dragging dead insects into the
nests as their booty, but suddenly the scene has changed. A
number of large red Amazon ants have come out on to the
surface of the nests. They hurry to and fro, clean their heads
and antennae hastily with their fore feet, and the rest of their
bodies with their middle and hind feet, and in doing so they
make comical leaps, and even turn head over heels. Then
they spring at one another, and strike one another on the
head with their antennae. Now they are ready for their war-
like expedition. Some Amazons take the lead, and are
followed by a whole army of several hundreds or thousands,
all in rapid march. Like a long red snake the robber band
marches in a narrow line, scarcely broader than a hand, straight
upon a nest belonging to their slave species (Formica rufibarbis),
some thirty yards away. Tidings of their approach have
already been brought, but too late ; a desperate resistance and
an attempt to barricade the entrances are of no avail. The
Amazons quickly make their way into the nest and seize the
pupae, killing only such opponents as continue to offer resist-
ance or refuse to loose their hold upon the pupae that they are
trying to save. With one bite the Amazon can drive its sharp,
sabre-like jaws through an enemy's head and pierce to the
XX, 1904, 347-375) ; 'An interpretation of the slave-making instincts in ants '
(Bullet. American Museum of Nat. Hist. XXI, 1905, 1-16); 'On the founding
of colonies by queen ants, with special reference to the parasitic and slave-
making species ' (Bullet. American Museum of Nat. Hist. XXII, 1906, 33-105).
K. Escherich, Die Ameise, Schilderung ihrer Lebensweise, Brunswick, 1906,
145-155.
1 Polyergus rufescens has as slaves either Formica fusca or F. rufibarbis, but
very seldom both at once. Near Exaten in Dutch Limburg I have always
found F. fusca as slaves, but near Mariaschein in Bohemia, near Vienna in
Austria, and in Luxemburg I have found only F. rufibarbis. The above
description refers to a day in July, 1892, when I was making some observations
in Lainz, near Vienna. In Switzerland Forel found both fusca and rufibarbis
living as slaves with Polyergus, but only in one instance in the same colony.
2 Formica rufibarbis is grey, with some red in the middle of its body.
It varies, however, very much in colour, for which reason I have described
it simply as a reddish grey ant, to distinguish it from the greyish black Formica
fusca.
A SLAVE-MAKING EAID 389
brain. In a few minutes the troop of red robbers emerges
from the plundered nest ; each Amazon is carrying in her
mouth an ant-cocoon, containing a pupa. The procession
returns to the robbers' nest, though not with such speed and
discipline as were displayed when they were marching to the
attack. The stolen pupae are adopted by the ants of the
same species, who are already slaves, and are brought up in the
Amazons' nest. When they develop, the ants, though born in
a robbers' nest, follow their own innate instincts as if they
were at home ; there is no compulsion, no tyranny on the
part of their masters. The whole * slavery ' consists in the
fact that the service, otherwise performed with a view to
the preservation of their own species, now benefits a race of
strangers. They not only attend to their young, but clean
and feed the Amazons themselves, for in their own home the
latter are such helpless creatures that they have forgotten
even how to feed themselves ! Thus, in the slave-making
instinct of the Amazons there is a cheerful as well as a gloomy
side, in fact the latter is the inevitable result of the former.
Just as the sabre-like jaw of the Amazon ant is an excellent
weapon in fighting, but quite useless for domestic work, so
their talent for warfare has been highly developed at the cost
of losing their normal instinct for self-preservation.
My object in laying this description before my readers is not
to amuse them with a highly coloured picture of the raids of
the slave-making ants, nor to discuss the psychological value
of their instinct,1 but rather to give a historical account of
slavery among ants, an account which includes in broad out-
lines all the phenomena that have been observed, and traces
both the origin of slavery and its development from the simplest
beginnings to its fullest perfection, and thence to its lowest
parasitical degeneration. The records that supply the materials
for this history are not written in any volumes, but on the
pages of the living book of nature ; they are biological facts,
that we must carefully compare and cautiously combine, in
order to learn from them the history of the slave-making
instinct, which has been developing from the early Tertiary
1 On this subject see Die zusammengesetzten Nester, &c., section 3, chapter i ;
also * Die psychischen Fahigkeiten der Ameisen ' (Zoologica, Part 26, Stuttgart,
1899); V ergleichende Studien iiber das Seelenleben der Ameisen, chapter ii ;
Instinkt und Intelligenz im Tierreich, 1905, chapters viii, ix.
390 MODEBN BIOLOGY
period to the present time. As long ago as the Miocene epoch
in the middle of the Tertiary period, there were a great many
genera and species of ants, resembling those of the present day
in their caste system and social organisation ; but forms
representing our slave-making ants have so far not been dis-
covered either among the fossils of Kadoboj in Croatia, or
among those found in amber from the Baltic and Sicily.1
We therefore cannot say exactly when the slave-making
instinct arose among ants, but as Europe, Asia, and North
America all possess, in common, several slave-making genera
and species of ants, differing only slightly in the development
of their instincts, we are led to the conclusion that at the
end of the Tertiary period, when the great continents of the
northern hemisphere were finally separated, the slave-making
instinct was already present, although it may have developed
further after their separation. We have nothing to rely
upon but the phenomena of comparative biology, when we
attempt to search into the manner in which slavery originated,
and to find out through what stages of evolution it has passed.
It is obvious therefore that the history of slavery, as sketched
here, is of a hypothetical character. It is a biological hypothesis,
but one that is based upon a solid foundation of facts, and offers
us a very natural explanation of them.
Fifteen years ago, in the last chapter of my work, ' Die
zusammengesetzten Nester und gemischten Kolonien der
Ameisen,' I discussed the origin and growth of the slave-
making instinct, and said that the problem seemed to be
insoluble. Observations made in the last few years in Europe,
North America, and the north of Africa have, however, revealed
a number of facts throwing considerable light upon the matter,
and bringing us at least a step nearer to the solution.
(a) Survey of the Biological Facts connected with Slavery
The biological material that we have to take into account
consists of the following nine chief groups of facts.
1 Cf. G. Mayr, ' Vorlaufige Studien iiber die Radoboj-Formiciden '
(Jahrbuch der k. k. geolog. Eeichsanstalt, XVII, 1867, Part 1) ; also by the
same author, Die Ameisen des haltischen Bernsteins, Konigsberg, 1868 ; C.
Emery, ' Le Formiche dell' ambra siciliana ' (Memorie d. Eeale Accad. d.
Scienze, Bologna, 1891, ser. 5, vol. I.).
FAQTS BEAKING ON SLAVEEY 391
1. A very great majority of the 4000 species of ants hitherto
described form new colonies thus : After the copulation
flight single impregnated females settle down alone, and
independently, without the assistance of strangers, bring
up their first brood. Among our native ants that found
colonies in this way are the greyish black Formica fusca and
its relative F. rufibarbis. All these species, if not interfered
with,1 live in simple colonies, i.e. in such as contain only ants
of one species. This method of founding colonies is undoubtedly
the oldest and most primitive.
2. There are certain species, particularly in the genus
Formica, of which the impregnated females after the copulation
flight cannot establish the new colonies alone, but need the
assistance of workers. Within this group we must dis-
tinguish two forms of colonisation ; in one, the workers
belong to the same species (2a), and in the other to a different
one (2&).
2a. Our red-backed wood-ants (F. rufa) and the black-
backed meadow-ants (F. pratensis) have many large and
populous nests, because their method of constructing their
nests out of dead vegetable matter is very well suited to circum-
stances of life in cold climates. Old colonies of these ants
consequently occupy a large district, which may include
several thousand square yards round the nests, and is traversed
by ant-tracks in various directions.2
If an impregnated female of such a colony alights after
the copulation flight on ground within this district, she has
no difficulty in finding workers of her own species, who either
take her back to her own nest, or proceed to establish with
her a fresh branch nest of the colony. This explains why
the queens of the species and subspecies belonging to the
same group as F. rufa, both in the Old and the New World,
have lost the instinct and ability to found new colonies inde-
pendently and alone. But what happens if a queen after her
copulation flight meets no workers of her own colony or of
1 I say : * if not interfered with,' because F. fusca and rufibarbis are stolen
as pupae by the slave-making ants, and so come to form mixed colonies
with them ; also because a colony, consisting normally of ants all of the
same species, may shelter guests or outcasts of other species.
2 For an account of giant nests and colonies of F. rufa see my Ursprung und
EntwicUung der Sklaverei, pp. 1 96, &c.
392 MODEKN BIOLOGY
her own species to assist her 9 If she is not to perish, she
will have to ask a shelter of the workers of some other species.
That this actually occurs in the case of our wood-ants (F.
rufa) I discovered near Luxemburg in the spring of 1906.
I found two recently established rufa colonies, one of which
contained only the queen of F. rufa and several workers of
F. fusca ; whilst the other had a rufa queen, and over a
hundred workers of both species. It seems that F. rufa and
F. pratensis seldom form joint colonies, but F. exsecta and
the North American exsectoides form them more frequently.1
There are therefore a number of transitions between this
group (2a) and the following (2b).
2fr. The impregnated females of some comparatively
rare species of sporadic occurrence, belonging to the rufa
group, regularly found their new colonies with the help of
the workers of another species of Formica, for they make
their way into small nests, and force the occupants to accept
them as queens. They can do this easily in colonies which
have lost their own queen by death. Near Luxemburg
I have observed new colonies founded in this way by the red
F. truncicola with workers of F. fusca.%
I did not only discover several mixed colonies of truncicola
and fusca at different stages of development, but I was able
to prove by actual experiment that a female truncicola, wander-
ing about after the copulation flight, was adopted as queen in
a fusca colony where there was. no queen. Wheeler has
observed the establishment of new colonies of F. consocians
in North America, when a female consocians has found her
way into a nest of F. incerta and has been welcomed there.3
In the case of other allied species of Formica, especially
such as, like consocians, have remarkably small females (e.g.
F. microgyna, nepticula, impexa, and montigena), Wheeler
has shown that in all probability they always establish their
colonies with the help of workers of another species. Even
among the Myrmicinae of North America there is a species
(Stenamma tenesseense) which is in the habit of allying itself
1 I found a colony of F. exsecta mixed with fusca near Luxemburg, in
October 1906.
2 Ursprung und Entwicldung der SMaverei, pp. 126-]31 ; supplement
(Part 19), pp. 650, &c.
3 A new type of social parasitism.
FACTS BEAEING ON SLAVEKY 393
with the workers of a closely related form (St. fulvum), when
it establishes new settlements.
The consequence of the adoption of a strange queen by
workers of another species is the formation of a so-called
' Adoption Colony.' After the queen's first brood has been
reared by the workers, the colony contains workers of two
distinct species, and thus becomes temporarily a mixed colony ;
but after three years the last of the workers who originally
adopted the strange queen dies,1 and the truncicola or con-
socians colony again becomes an ordinary colony, containing
only one species of ant, and as such it continues to grow,
and in the course of ten years it may be inhabited by many
thousands of ants.
This method of founding truncicola colonies leaves, however,
some trace upon the class of workers, the first three generations
of whom are reared by F. fusca, and the last of these truncicola
may be still alive in the sixth year after the colony was founded.
After the F. fusca have all died out, the truncicola workers
retain a tendency to rear the pupae of fusca, although they
devour those of other kindred species, or kill the newly developed
ants as strangers. This remarkable instinctive preference
shown by F. truncicola for the fusca pupae is due to the fact
that the two species once lived together in one colony, as I
discovered in 1904 from experiments with a young colony
of F. truncicola that I kept in a room,3 and the results were
confirmed in 1906 by other experiments with an old colony
of the same ants.
Let us now suppose F. truncicola to be an ant living chiefly
on stolen pupae of other ants. What kind of selection would
it make among the pupae stolen under natural circumstances ?
It would rear the pupae of that species alone by which it
had itself been reared, viz. F. fusca. We should thus have
the identical circumstances which actually prevail in the
case of the red robber-ant (F. sanguined). This explains
how their extraordinary instinctive choice of the fusca pupae
may have originated ; for F. sanguinea also as a rule establishes
new colonies with the help of fusca workers.
1 Numerous observations and experiments that I have made, show that
the workers of Formica live from two to three years.
2 Ur sprung und Entwicklung der Sklaverei, pp. 125, 167.
394 MODEKN BIOLOGY
Let us now return to our survey of the biological materials
for a history of slavery amongst ants.
3. Among the relatives of F. truncicola there are several
species whose queens found colonies in the same way as those
described as group 26 — namely with the help of workers of
another species — but the colonies remain permanently ' mixed,'
for as soon as the ' primary ' assistants die out, they are
replaced by ' secondary ' workers of the same species as
those who participated in the foundation of the colony ;
FIG. 45. — Worker of the blood-red robber-ant. (Formica sanguined)
(3£ times the natural size).
these secondary workers being obtained by means of a slave-
making raid. The red robber-ant, F. sanguinea, in Europe
and Asia forms mixed colonies of this kind, and so do the
North American subspecies F. rubicunda, subintegra, &c.
It is probable that other North American species, F. dakotensis
var. Wasmanni and F. Pergandei, also belong to this class. ,
My observations, carried on during twenty years, show
that the typical F. sanguinea (fig. 45) has slaves in
almost all its colonies ; these slaves mostly are F. fusca,
seldom rufibarbis, and still more rarely both species are mixed.1
1 I have suggested an explanation of the presence of two kinds of slaves
in one colony in Ursprung und Entwicklung der Sklaverei, p. 209.
FACTS BEAEING ON SLAVEKY 395
Only the most populous colonies — on an average one in
forty — contain no slaves, because the assistance of strangers
is not required in them. Wheeler thinks that the North
American red robber-ant F. rubicunda possesses the slave-
making instinct in a rather lower degree, and his opinion
has recently been confirmed by H. Muckermann, S. J.1
Near Prairie du Chien (Wisconsin) Muckermann examined
eleven colonies of these ants, and found six containing slaves,
mostly F. subsericea (which is, like F. subaenescens, a variety
of our F. juscd), and less frequently F. nitidiventris or subae-
nescens, whilst the other five nests contained no slaves. The
instinctive desire to steal fresh slaves and bring them up
seems therefore to cease earlier in this North American robber-
ant than in our European F. sanguinea ; perhaps it dies out as
soon as the colonies have attained a certain size. Forel
described a subspecies of robber-ant in Canada, which he
believed to have no slaves at all, and named for that reason
aserva or slaveless. In the United States, however, Wheeler
examined eight or nine colonies of these ants and found one
containing a few slaves. It is certain that this sanguinea
subspecies has slaves much less often than its nearest relative
F. rubicunda. The North American varieties of the blood-red
robber-ant still at the present day represent the transitional
stages leading to the highly developed slave-making instinct
possessed by our European and Asiatic F. sanguinea.
The North American F. dakotensis occupies a peculiar
position midway between the species of the rufa group and
those of the sanguinea group. In biological respects also
it greatly resembles the latter. According to the careful
observations made by Muckermann and Wolff, S. J., at Prairie
du Chien, in thirteen colonies of F. ddkotensis var. Wasmannl,
five contained no slaves, the remaining eight had F. subsericea
as their assistants. All the colonies of Wasmanni in which
slaves were found were on the left bank of the Mississippi,
and all in which there were no slaves were on the right bank.
It was not possible to determine which of the former were
still adoption-colonies, and which were robber-colonies, that
had supplied their need of workers by stealing pupae of another
species.
1 Cf. Biolog. Zentralblatt, 1905, No. 19, pp. 651, &c.
396 MODERN BIOLOGY
In their origin all the slave-keeping colonies mentioned under
3, both those of the red robber-ants in Europe and North
America and those of F. dakotensis var. Wasmanni, are
adoption-colonies, arising out of the association of an impreg-
nated female belonging to the ruling species with workers
of the auxiliary species.1
They differ from the colonies mentioned under 26 only
in becoming subsequently robber-colonies, as the workers
of the ruling species procure new assistants of the same species
as those which originally helped to form the colony — fresh
slaves being obtained by raids, when the first die out, as
long as slaves are needed at all to strengthen the
settlement. Mixed adoption-colonies are only of a tem-
porary nature, and last but three years, then they give
place to more or less permanently mixed colonies of slave-
making ants.
In both the temporarily and in the permanently mixed
colonies, a new colony is founded by an impregnated female,
who makes her way into a nest belonging to another species,
and takes up her abode there, whether the workers receive
her willingly and promptly, or whether they are forced to
accept her against their will and after much hostility. There
are a great many different degrees between a peaceful reception
and a violent intrusion.2
1 As our F. sanguined has often several nests belonging to one colony,
it frequently happens that an impregnated female after the copulation flight
forms a new nest with the help of workers belonging to the same colony.
In this case there is no new colony, but a new branch of the same colony, as
we saw with regard to F. rufa and pratensis (2a). Cf. also Ursprung und
EntwicUung der Sklaverei, 1905, p. 201.
2 In 1905 and 1906 Wheeler made experiments with a North American sub-
species of the red robber-ant, F. rubicunda, and expressed the opinion that the
impregnated queen after the copulation flight forces her way into a nest of slave
ants, kills or drives out the workers, and takes possession of their pupae, which
she brings up as her first assistants. But as Wheeler's experiments were
all made with unimpregnated females which he had taken out of rubicunda
nests, his observations afford no evidence of the manner in which rubicunda
colonies are formed. According to my experience with European red robber-
ants, the young unimpregnated females are very quarrelsome, and occasionally
take part in carrying the larvae and pupae in the observation-nests. They
have, therefore, characteristics of workers, which are absent in the impregnated
females. Moreover, an impregnated female, who may become the foundress
of a new colony, has a far better chance of being made welcome in a colony
without a queen than an unimpregnated. Experiments with the latter
cannot refute the adoption hypothesis. In the case of another North American
subspecies of the same robber-ant, F. subintegra, Wheeler himself thinks we
must believe that it may find admission into weak colonies of the slave species,
FACTS BEAEING ON SLAVERY 397
There are also many grades between the adoption of a
queen belonging to the ruling species in a weak colony of the
auxiliary species, and the alliance of a queen of the former
species with a queen of the latter, who is engaged in founding
a nest and has no adult workers.1
The ants belonging to group 3 are distinguished from
those of the next group (4), which also live in permanently
mixed colonies, by the fact that the masters are still essentially
independent of the slaves, and only begin to keep slaves when
their colony has attained considerable strength. Among our
European F. sanguinea this occurs seldom, and only in the
most populous colonies, but it is of much earlier and more
frequent occurrence among the North American representatives
of the species. The latter form a natural link between group 3
F. subsericea. Of course one queen by herself of whatever species — sanguinea or
truncicola or consocians or rufa — can find admission to the nests of a slave
species only under exceptionally favourable circumstances. These conditions
seem particularly difficult in the case of F. sanguinea, but even here there are
undoubtedly many grades between voluntary and compulsory admission,
and complete failure to obtain it. During the summer of 1906 I made experi-
ments with fifteen young queens of sanguinea, caught directly after their
copulation flight, with a view to observing their reception among F. fusca,
pratensis, &c. The result was a confirmation of my adoption theory and a
refutation of Wheeler's raid hypothesis. Full details of these experiments
will be published elsewhere, as well as of others with rufa and pratensis queens.
In 1904 Emery suggested that new Polyergus colonies might be formed
if a queen forced her way into a slaves' nest, took possession of their pupae,
and reared them as her assistants. As even the Polyergus workers have lost
their instinct to rear their own young, it seems that this hypothesis is still less
probable in their case than in that of Formica sanguinea. No such proceeding
has been observed under natural conditions on the part of either Polyergus
or Formica, but only on that of Tomognathus (by Adlerz). The last-named
genus belongs to quite a different subfamily of ants, and their whole slave-
making instinct is completely unlike that of the other two genera. (Cf.
Group 5.)
1 Forel's * Allometrosis ' (alliance between queens of different species)
supplies at least a possible way of accounting for the origin of mixed colonies
of Formica. On June 6, 1906, at Osling, near Hoscheid in Luxemburg, I
discovered under one stone a queen of F. pratensis (var. truncicolo -pratensis)
and a queen of F. rufibarbis close together, and I took them both away with
me. I put the pratensis queen in a nest with thirty workers of the F. fusca,
who for several days pulled her about and ill-treated her. In order to save
her life, I took her out, and put her into a nest, where I had the rufibarbis
queen under observation. She at once approached the latter, began to stroke
her with her antennae and to ask for food, as if they were friends. This scene was
repeated several times during the day, and on the following day they sat close
together, but on the third day the rufibarbis queen died of exhaustion, whilst
the pratensis queen had completely recovered. These observations seem to
show that when two queens form an alliance, the one belonging to the auxiliary
species may be got rid of in a peaceful manner, after she has reared her first
brood of workers so far as to be of service to the other queen in founding her
colony.
398
MODEEN BIOLOGY
and the preceding group (26), in which no fresh slaves are
procured after the ants that originally helped to found the
colony have died out.
4. Closely allied with the genus Formica, though differing
from it in some important points, is the very interesting genus
Polyergus, with which we have already made acquaintance
(p. 387). The chief difference is in the upper jaw, which
FIG. 46.
a. Head of the blood-red robber-ant (Formica sanguined).
b. Head of the red Amazon-ant (Polyergus rufescens).
(6 times the natural size.)
in the Amazon ants (Polyergus) is shaped like a sabre, and
has no indentations. (Of. fig. 466 with 46a.) Polyergus rufe-
scens is the European representative of this genus. Fig. 47
shows the ergatoid queen1 and fig. 48 the worker of the European
Amazon. There are four other subspecies in North America,
Polyergus lucidus, breviceps, bicolor, and mexicanus^ In their
habits they resemble the European Amazon, although closer
1 The ergatoid queen of Polyergus is a real queen in the dress of a worker.
She resembles the workers, however, only in the structure of the abdomen
and in being wingless. Cf. ' Die ergatogynen Formen bei den Ameisen und
ihre Erklarung ' (Biolog. Zentralblatt, 1895, Nos. 16 and 17, pp. 606, &c.).
2 Of these subspecies bicolor resembles F. sanguinea in colouring, and has
rather broader jaws than our P. rufescens. The genus Polyergus is marked
off from Formica at the present time by a definite morphological distinction,
which will be explained in the second part of our examination of the two
genera. The slaves of the North American Polyergus belong to various
species and subspecies of the groups to which F. fusca and pallide-fulva
belong.
FACTS BEAKING ON SLAVEKY
399
investigation may perhaps reveal many instructive degrees in
the development of the slave-making instinct in their case,
as in the subspecies of F. sanguinea. The mode of life of P.
rufescens is that of which most is known at present, so, in
considering the biological characteristics of this group (4), we
must limit ourselves to it.
The mixed colonies formed by the Amazons and their
FIG. 47.
FIG. 48.
FIG. 47. — Ergatoid queen of the Amazon ant (Polyergus rufescens} (3J times
the natural size).
FIG. 48. — Worker of the Amazon ant (Polyergus rufescens) (3| times the
natural size).
slaves do not differ essentially from those of the two previous
groups in the manner of their formation. They are at first
adoption-colonies, resulting from the association of an impreg-
nated female of the ruling species with workers of a definite
slave species ; l and the Amazons subsequently rob the nests of
this same species, when they make raids to obtain fresh slaves.
Colonies of Polyergus, founded with the help of F. fusca,
afterwards rob fusca nests ; those founded with the help of
F. rufibarbis choose rufibarbis nests as the normal goal of their
slave hunts. In ' Les Fourmis de la Suisse ' (pp. 287, &c.),
1 The colony mentioned by Forel (Lesfourmis de la Suisse, p. 302, No. 18),
in which Polyergus and rufibarbis were found together, was probably an
adoption-colony of this kind. Experiments made by both Forel and myself
with isolated Polyergus queens have shown that they obtain admission with
comparative ease to the nests of the slave ants. (Cf. Die zusammengesetzten
N ester, 1891, pp. 84-87.)
400 MODEKN BIOLOGY
Forel describes his observations of Amazons with fusca and
rufibarbis slaves, and says that in the same region their military
tactics varied somewhat according to the species kept as
slaves. Amazons with rufibarbis slaves march more quickly
and in more regular lines, as they have to attack enemies
better able to offer resistance than the fusca.
The robber-colonies of the Amazon ants differ, however,
from those of the red robber-ants and their relatives in one
important respect, viz. that the masters are absolutely depen-
dent upon their slaves. The Amazons can steal slaves, but
they are incapable of working and of leading a normal, inde-
pendent existence. Their helplessness finds expression in
their sabre-shaped jaw and in the decay of their domestic
instincts, which is carried to such a point that they will starve
with food before them, if they have no slaves to put it into
their mouths. The absolute dependence of the Amazons
upon their slaves is shown also in the biological fact that in
their nests the number of slaves is very great in comparison
with that of the masters, the slaves being often from five to
ten times as numerous. The Amazons steal as many slaves
as they can, the red robber-ants only as many as they need to
supply the deficiency in their own numbers. This is the reason
why among the Amazons the number of slaves is proportionate
to that of the masters in the same nest, whilst in the nests
of the red robber-ants the numbers are in inverse ratio ; in
the former case — the more masters, the more slaves ; in the
latter — the more masters, the fewer slaves.1 With the
genus Polyergus we reach the end of the evolution of the slave-
making instinct in the subfamily of Formicinae (Camponotinae).
It culminates psychologically and morphologically in the
Amazons with their sabre-like jaws and their talent for war,
but there are in them unmistakable signs of degeneration.
We shall be able to trace the different stages leading down to
social parasitism, when we compare them with the slave-
robbers of the genus Strongylognaihus among the Myrmicinae,
in the sixth and seventh parts of our investigation.
Let us now turn to the subfamily of the Myrmicinae.
5. A quite peculiar and altogether isolated position among
slave-making ants is occupied by the northern genus Tomo-
1 Vergleichende Studien iiber das Seelenleben, &c., p. 52.
FACTS BEARING ON SLAVEEY 401
gnathus, which occurs both in Northern Europe and in North
America, and takes its slaves from the closely allied genus
Leptothorax.1 The former genus differs from the latter
chiefly in having broad mandibles devoid of labium and not
indented, whence its name Tomognathus (cutting jaw), also
it is much larger than any Leptothorax. According to observa-
tions made by Adlerz in Sweden, the females of Tomognathus
sublaevis, that bear an extraordinary likeness to the workers,
and have no wings, make their way into the nests of Leptothorax
acervorum or muscorum, drive out the inhabitants, and take
possession of the young brood, which they rear in the stolen
nests. In this way mixed colonies of Tomognathus and
Leptothorax are formed, in which winged specimens of the
slave species often occur, and so these colonies differ remark-
ably from the other robber-colonies of slave-making ants.3
Tomognathus is probably descended phylogenetically from
the genus Leptothorax, to which its slaves belong. The evolution
of its slave-making instinct is therefore certainly not con-
nected genetically with that of Formica and Polyergus, and
perhaps it is not connected with that of the following groups.3
6. The Myrmicine genus Strongylognathus is a miniature
reproduction of the Amazons of the Polyergus genus described
under group 4. The sabre-shaped jaw accounts for the name
sabre or scimitar-ants, which has been given to this genus.
It occurs near the Mediterranean and in western Asia ;
only one species, Strongylognathus testaceus, is found in Central
Europe, and the genus is not represented in the north. We
are not now concerned with the Central European species, as
it does not make slave raids, but we must examine its southern
connexions, Str. Huberi in the south of Europe and the north
of Africa, and Str. Christophi in the districts east of the
Mediterranean and on the Kirghiz steppes.
1 Tomognathus sublaevis was found not long ago by Viehmeyer in Saxony.
It belongs, therefore, to the fauna of Germany.
2 Near Exaten in Holland, in nests of F. sanguinea, I have occasionally,
but very rarely, found one or two winged females of fusca. (In colonies No. 55
and No. 235, i.e. in two out of 410 colonies.)
3 It is still doubtful whether the genus Myrmoxenus, discovered by Ruzsky
on the steppes of the south-east of Russia, is connected with Tomognathus or
Strongylognathus. Myrmoxenus Gordiagini always forms mixed colonies
with Leptothorax serviusculus. We do not yet possess any detailed observa-
tions of their way of life.
2 D
402 MODERN BIOLOGY
Like the Amazons, these two species of scimitar-ants are
superior to their slaves in size and strength, their colonies
also contain a considerable number of both masters and slaves,
and they too organise regular slave-hunts, which are, however,
in the case of the scimitar-ants directed against the nests of
the little turf-ants (Tetramorium caespitum). All the species
of Strongylognathus have some species of Tetramorium as slaves
in their mixed colonies.
Forel found Str. Hubert in the south of the Valais and in
Tunis, but he was not able to study their slave-hunts under
natural conditions, though he did so in artificial nests. In
the summer of 1904 Escherich sent me a colony of these ants
from Fully in the Valais, and after I had brought them into
contact with some large Tetramorium colonies in Luxemburg,
they attacked the latter, put them to flight and carried off
their pupae. That the same colony under its natural conditions
in the Valais had acted in the same way was proved by the
fact of its containing, when it reached me, two subspecies of
Tetramorium slaves, one larger than the other. As in this
species the workers of one colony are all of the same size, it
follows that the original slaves of the scimitar- ant colony
must have belonged to one only of these subspecies, and. the
other must have been introduced by a raid upon some Tetra-
morium nest of a different subspecies.
Not long ago Eehbinder observed the scimitar-ant of the
south-east making a raid under natural conditions, near the
monastery on Mount Athos. This ant is the Str. Christophi
var. Behbinderi, which is remarkable for its size. It is bigger
and stronger than Huber's scimitar-ant, and better able to
conquer the stubborn Tetramorium in a pitched battle. We
may therefore assume that, in its development of the slave-
making instinct, it stands on a level with Polyergus, whereas Str.
Huberi probably ranks rather lower, owing to its inferior size
and strength ; we may, however, regard it as a genuine slave-
maker.
7. Let us now turn to the little yellow Str. testaceus, the
northern relation of the former species, to which it is greatly
inferior in size and strength, being no larger than the little
turf-ant, with which it lives in mixed colonies.
I have studied its habits both when at liberty and when
FACTS BEAEING ON SLAVEEY
403
living in nests that I had arranged for purposes of observation,
in Holland, Bohemia, Luxemburg, and near the Ehine, and I
have come to the conclusion that it is no longer capable of
making slave-raids. But, if this is true, how can we account
for the great number of slaves in its mixed colonies ? The
number of slaves is relatively much greater than in the Sir.
Huberi nests, although the average number of masters is
smaller, often scarcely reaching a hundred, and seldom being
more than a few hundreds. In the nests of Str. testaceus there
are generally from five to ten times as many slaves as masters.
FIG. 49. — Yellow scimitar-ant (Strongylognathus testaceus)
(12 times the natural size).
How does this little ant obtain its numerous slaves, if it is no
longer capable of fighting successfully against the strong
colonies of turf-ants, who have a hard chitinous covering and
a dangerous sting ? What is the solution of this problem ?
I was able to suggest a probable solution after making a
number of observations near Prague in Bohemia in 1890 and
1891. In two of the mixed Strongylognathus and Tetramorium
colonies there, I found a queen of the latter species ; l in one
of these colonies there were even pupae of the winged males
and females of both species. I drew the following inference
from these facts.
1 It is well known that the Tetramorium queens are very difficult to find even
in independent colonies ; it is possible to discover them only when the nest
is in an exceptionally favourable situation.
2 D 2
404 MODEKN BIOLOGY
The little yellow scimitar-ant does not obtain its slaves by
stealing them, but after the copulation flight an impregnated
female seeks the company of a Tetramorium queen, who has
withdrawn under a stone in order to establish a new colony
there. The young workers of Tetramorium thus rear the brood
of the Strongylognathus queen as well as that of their own
queen. As the Strongylognathus males and females are much
smaller than those of Tetramorium, the latter show preference
to their larvae and neglect their own, which require more food
and attention. The little larvae of the workers of both
species are reared with equal care. That the number of
Strongylognathus workers is small in comparison with that of
Tetramorium workers is best explained by the fact that this
caste is no longer necessary to Str. testaceus for the preservation
of its species, and is therefore gradually approaching extinction.
In every colony the winged males and females of Strongylo-
gnathus are actually in the majority.
The mixed colonies, formed by our northern yellow scimitar-
ant with the turf-ant, are therefore the result of an alliance
between two queens of the different species. But were they
not formerly robber-colonies ? Otherwise what is the meaning
of the scimitar-shaped mandibles possessed by these little
ants, which so completely resemble those of the southern
members of the same genus, as well as those of the Amazons
and other ants in which the slave-making instinct is highly
developed ? Did not our little yellow ant once use these formid-
able mandibles, when it was itself bigger and stronger, to crush
the hard head of an enemy in battle, as its relatives still do ?
What was the use of these peculiar weapons, if the scimitar-
ants have always lived in peaceful alliance with the turf-ants ? l
There can be no doubt that the ancestors of Str. testaceus
used to steal their slaves, just as their larger kinsfolk still do in
the south. The original home of the Strongylognathus genus is
in Southern Europe, where four species occur — Huberi, Chris-
tophi, Caeciliae, and afer ; our little yellow scimitar-ant is an
isolated northern offshoot of this group ; and the fact of its
•migration northward gives us a very simple clue to the reason
1 This difficulty cannot be removed by a reference to the umiotched mandibles
of the males of many genera of ants, for these mandibles are often small and
weak, and not at all what we mean by scimitar-like.
FACTS BEARING ON SLAVERY 405
why it has lost its slave-making instinct. All our slave-
keeping ants without exception hunt their slaves only during
the hottest hours in the summer months. If a southern slave-
hunter migrated in a northerly direction, its slave-making
instinct would be felt at longer and longer intervals until it
finally died out altogether. This would be more likely to
occur, if at the same time the size of the ant's body diminished,
so that it gradually lost the power to seize its enemy's head
and crush it between its jaws. In the Strongylognathus workers
the instinct prompting them to steal the turf-ants' pupae to
be their slaves gave place to an instinctive desire on the part
of the impregnated females to ally themselves with turf-ant
queens in order to establish colonies together.
But is this latter instinct something new in the history of
Strongylognathus colonies ? No, it is very old, for, as I have
shown in discussing group 2&, it was the motive that led
primarily to the development of the slave-making instinct.
Even at the present time all robber-colonies of slave-keeping
ants begin by being adoption-colonies, and owe their origin to
impregnated females of the ruling species, who, having made
their way to a weak nest of the subject species, obtain admission
to it. It is only at a subsequent period that the descendants
of these females procure fresh slaves by plundering the nests
belonging to the species that originally co-operated in founding
the colony.
The mixed colonies formed by the little yellow scimitar-
ant and its Tetramorium slaves differ from those of its slave-
keeping relatives l only in the fact that the queen of the slave
species remains alive, and thus the masters are supplied with a
constant succession of fresh slaves, but they are all born in
the same nest, and the slaves are no longer stolen. The allied
1 The distinction may be expressed in other words as follows : The queens
of slave-keeping ants, when about to found new colonies, choose by preference
those colonies of the slave species which have lost their own queen, or rather,
as a rule, it is only to such colonies that they obtain admission. The Strongy-
lognathus testaceus queen, however, finds admission most readily to a young
colony of the slave species, which has only just been established, and where
there are no full-grown workers with the queen. In both cases the instinct
that prompts the queen to seek out a nest belonging to the slave species is
due to the same causes, viz. to an impulse to force a way into a nest of strange
ants, and to her sense of smell, which draws her to the nest of her normal
slave species as being particularly attractive. All the other conditions of
her reception depend, not on the instinct of the queen who seeks admission,
but on that of the ants that grant it.
406
MODERN BIOLOGY
colonies of Sir. testaceus and Tetramorium caespitum are
characterised by their remaining permanently at a stage,
which is only temporary in the case of the robber-colonies.
The loss of the slave-making instinct has caused a reversion
to an early stage, preceding the development of the slave-
making instinct.
8. There are some remarkable ants that have no caste of
workers, but live as parasites with other species. All these
belong to the systematic subfamily of Myrmicinae.
As long ago as 1874, in ' Les fourmis de la Suisse,' Forel
mentioned some extraordinary males and females of a Myrmica,
FIG. 50. — Wheeleria Santschii (female)
(6 times the natural size).
which had been found in the Alps in a nest of Myrmica lobicornis,
but which were totally unlike the males and females of this
species. He proposed calling these peculiar creatures Myrmica
myrmicoxena, and expressed the opinion that they lived as
parasites in the colonies of other species of Myrmica.
It is still somewhat doubtful whether Myrmica myrmicoxena
is really a parasitic species, but Santschi's observations in
Tunis have recently revealed the existence of a very interesting
parasitic ant in North Africa, described by Forel under the
name of Wheeleria Santschii) which lives as a parasite in the
nests of Monomorium Salomonis and its varieties.1
1 Cf. Aug. Forel, Miscellanea Entomologiques, II, 1895, and Mceurs des
fourmis parasites, 1906. See also list of works on p. 387, note 2.
PARASITIC ANTS 407
The species consists only of males and females, both winged.
The female (fig. 50) l loses her wings after impregnation, and
then enters a Monomorium nest, whence at first she is often
driven out ; but she persists in returning and finally obtains
admission. Thereupon the Monomorium workers, preferring
to wait upon the new little queen than upon their old large one,
kill the latter, and devote" themselves to rearing the brood
of their parasite. The Wheeleria males and females, brought
up in a Monomorium nest, pair with one another within the
nest, and then the impregnated females depart, in order to
force their way into other colonies of Monomorium and to
exact service from their occupants. The mixed colonies
of Wheeleria and Monomorium, as Santschi's observations
and experiments have shown very clearly, were originally
adoption-colonies.
In North America there are three genera of the subfamily
of Myrmicinse, of which males and females are known, but
no workers. According to Pergande and Wheeler's observa-
tions, they all live as parasites in the nests of other species
belonging to the same subfamily. Epoecus Pergandei lives
with Monomorium minutum var. minimum, Sympheidole
elecebra with Pheidole ceres, Epipheidole inquilina with PJieidole
pilifera var. coloradensis.
We must assume that the North African genus Wheeleria,
and the three genera just mentioned of North American
parasitic ants, formerly possessed a caste of workers, like
all normal ants. History is silent as to the loss of this caste,
but it must have been lost in one of two ways. Either the
ants were once peaceful guests living with their hosts, as
Formicoxenus nitidulus still does in Europe, and Leptothorax
Emersoni and Symmyrmica Chamberlaini do in North America,
or they used at one time to be robbers, stealing the pupae
of their slave species, but subsequently forming permanent
colonies in alliance with them, as Strongylognathus testaceus
does with the turf -ants (group 7). We must leave it to future
research to determine which of these two explanations is
correct, but in either case the fact that these ants lived with
others of a different species would render the preservation
1 The illustration is from a photograph of a specimen kindly sent me by
Santschi.
408
MODEBN BIOLOGY
of their own workers superfluous. The disappearance of
this caste has reduced them from the position of guests
or masters to that of parasites, living upon their former hosts
or slaves.
They have not, however, reached the lowest degree of
parasitism, for their winged males and females are normal,
although they already show peculiarities which may be regarded
as indicating degeneration.1
9. Let us now return to European ants.
All over Central and Northern Europe there occurs—
though it is very rare — a strangely degenerate little ant,
Anergates atratulus, which lives in mixed colonies with workers
FIG. 51. — Male of Anergates atratuljis
(12 times the natural size).
of the turf-ant (Tetramorium caespitum). This genus is
called ' worker-less ' (Anergates) because it possesses no workers.
The winged, black females are fairly normal, but when, as
queens, they have lost their wings, their bodies gradually
assume the circumference of a small pea, and they pass into
a state known as physogastry.
The little yellow males are thoroughly degenerate ; not
only have they no wings, but in shape they resemble an ant
pupa rather than an adult. As Adlerz and I have frequently
observed, copulation takes place within the Tetramorium
nest, and the impregnated females then fly away, in order
to discover new Tetramorium colonies and obtain admission
to them. That very few of the hundreds of females issuing
1 Cf. Emery, * Zur Kenntnis des Polymorphisnms der Ameisen ' (Biolog.
Zentralblatt, 1906, No. 19, pp. 624-630). *
PARASITIC ANTS 409
from a colony of Aner gates and Tetramorium succeed in this
endeavour, is proved by the rarity of Anergates.
Various hypotheses have been brought forward and numerous
experiments have been made, to account for the origin of
mixed colonies of Anergates and Tetramorium at the present
day, but no one as yet has succeeded in actually observing
the establishment of such a colony. It is probable that these
mixed colonies are adoption-colonies, like those mentioned
in group 8. An impregnated Anergates female forces her
way into a weak Tetramorium nest, where there is no queen,
or into a branch nest of a larger colony, and is there adopted
as queen. It may be that the turf-ants kill their own large
queen after adopting the little parasite ; if so, their action is
analogous to that of Wheeleria as observed by Santschi
(see p. 406).
It is difficult to say how such a colony can be maintained
permanently unless fresh workers of the turf-ant are produced,
for in the mixed colonies of Anergates and Tetramorium no
queen and no worker pupae of the latter species have ever
been discovered.1
Moreover, it is still uncertain whether such a colony lasts
for over three years, and also whether the Tetramorium
workers may not live longer than that time. As far as we
know so far, we have to regard these colonies of Anergates
and Tetramorium as adoption-colonies, that remain permanently
at a stage which is only temporary in the case of colonies of
slave-keeping ants.
Was Anergates atratulus always a parasite, possessing no
workers ? Were the males always wingless creatures, re-
sembling pupae, and showing unmistakable marks of degen-
eration ? Were these ants originally created in this state
of absolute dependence upon their slaves, or are they de-
scended from another genus, capable of an independent
existence ? It is- impossible not to decide in favour of the
latter alternative, although the history of Anergates, and the
process which has led to its parasitical degeneration, are still
very obscure.
1 In 1904 I placed some worker pupae from other Tetramorium nests in a
colony of Anergates and Tetramorium, but the slaves of the latter species
would not rear them, and either ate them or threw them away.
410 MODERN BIOLOGY
Let us compare this parasitic ant without workers, with
the little yellow scimitar-ant (group 7). Both live as parasites
in the nests of the same turf-ant. Sir. testaceus is not found in
the north of Europe, although A. atratulus occurs there.
The former has not yet lost its worker caste, but the workers
are far less numerous than they are among the southern
slave-keeping representatives of the genus, and Anergates
has none at all. Let us imagine that some species of ant,
at the same stage of development as Sir. testaceus, penetrated
northwards in some remote age, and the loss of activity and
energy, due to the colder climate, led to degeneration in a
creature coming from the south. The dependence of the
masters upon their slaves would constantly increase until finally
the workers of the former species died out, having ceased to
be necessary for the preservation of the species. Thus there
would exist between our ant and the turf-ant, with whom
it lives, a relation similar to that now existing in North Africa
between Wheeleria and Monomorium. The males and females
of the parasitic ant would correspond to the normal winged
males and females of other ants, as they do in Wheeleria,
and if this genus sank into still deeper parasitical degeneration,
they would finally resemble Anergates.
The Anergates males are so little able to move, being
wingless and like pupae, that they cannot leave the nest,
and thus many are saved from the destruction that overtakes
most ants on the occasion of their copulation flight. The
degeneration of the males becomes in this way a hindrance
to the extinction of the species. On the other hand, the
physogastry of the female increases her fecundity. Both
peculiarities — absence of wings and resemblance to pupae
on the part of the males, and physogastry on the part of the
females — serve the same end, and indicate a last desperate
attempt to preserve the species.
Need this hypothetical account of the evolution of Anergates
be regarded as purely fantastic ? No ; for if we once
allow that this parasitic ant was not created in its present
degenerate condition, we have no choice but to admit that
it has reached this condition by a retrograde evolution,
produced by a series of either perceptible or imperceptible
changes.
THE SLAVE-MAKING INSTINCT 411
(b) Inferences respecting the Development of the Slave-making
Instinct
We have now completed our survey of the biological
facts relating to slavery among ants. What conclusions
may we draw from these materials ?
They have been clearly indicated in the foregoing pages.
If we attempt to give a natural account of the origin of the
conditions described in groups 1-9, and still actually existing,
we cannot possibly avoid regarding them from the point of
view of the evolution theory. It alone is able to give us a
clue that will guide us to an understanding of the various
phenomena.
Not only are the colonies of slave-keeping ants adoption-
colonies in their origin, but they must phylogenetically be
descended from similar colonies, mixed for a time only, such
as we have considered in group 26. This overthrows once
for all Darwin's very ingenious, but unsuccessful attempt
to account for the origin of slavery by assuming that the
stolen pupae of strange species chanced to be reared by mere
accident,1 and it substitutes a much more probable and
intelligible explanation.
The progressive development of the slave-making instinct
must have passed through the phylogenetic stages presented
to us at the present day by Formica and Polyergus in groups
3 and 4 respectively. After the culminating point was
reached, retrogression must have set in, on the analogy of
groups 5-9, and have led to the lowest depth of parasitism,
after which nothing remains but the extinction of the species.
We know from the evidence of palaeontology that in the
course of the world's history many thousands of species have
perished, though few perhaps have had so easy a death as
that which awaits Anergates, possibly after some thousands of
years.
I may be asked whether we are to regard the history of
the slave-making instinct in ants, illustrated by groups 1-9,
as a uniform process of evolution, uniting the present
1 A fuller proof of the futility of this theory may be found in chapter i of my
' Ursprung und Entwicklung der Sklaverei bei den Ameisen ' (Biolog. Zentral-
blatt, 1905, Part 4).
412 MODEEN BIOLOGY
representatives of these nine groups into one single genealogical
line. This would mean that the present slave-stealing genus
Strongylognathus (group 6) was descended from Tomognathus
(group 5), and this again from the present Amazons of the
genus Polyergus (group 4) ! In fact, we ought to regard
Anergates (group 9) as the descendant of a species of still-
existent Formica belonging to group 2 !
No thoughtful biologist has ever imagined, or ever will
imagine, anything of the kind ; for Polyergus and Strongylo-
gnathus, Formica, and Anergates belong to distinct subfamilies
of ants, and cannot be closely related to one another. Another
suggestion is, that within the same subfamily the present
representatives of the successive biological groups may be
directly descended from one another. Shall we, for instance,
derive the Amazons of the present day from the red robber-ants
of the present day, and these again from F. truncicola of the
present day ?
An attempt to do this would display complete misunder-
standing of the process of evolution that I have described. I
have suggested that our present Amazons once passed through
a stage in the history of their race, resembling the present
stage occupied by the red robber-ants, as far as the slave-
making instinct is concerned. Also, I think that the red
robber-ants, which now form with their slaves permanently
mixed colonies maintained by slave-hunts, once passed through
a stage resembling that at which F. truncicola has now arrived,
when the mixed colonies were only temporary. We must
view in a similar way the connexion between the other succes-
sive groups that we have considered as furnishing materials
for an account of the growth of slavery amongst ants. This
is plainly quite a different theory and is free from the objections
mentioned above.
The development and growth of the slave-making instinct,
from its simplest beginnings to the parasitical degeneration
due to it, may be illustrated by the nine groups that we have
considered, but I must again lay stress upon the fact that
they do not form one single sequence in evolution, and are
not descended directly from one another. The common
historical origin of the whole family of ants, and their historical
connexion with other families in the order of Hymenoptera
THE SLAVE-MAKING INSTINCT 413
is based upon other arguments, supplied by comparative
morphology, and has nothing directly to do with our biological
question.
Slave-keeping ants of the subfamily Formicinae can phylo-
genetically be derived only from other Formicinse, that formerly
led an independent existence ; and in the same way slave-
keeping or parasitical Myrmicinae can only be derived from
other Myrmicinae, that once led an independent existence. For
this reason, at the close of my account of the fourth group, I
drew attention to the fact that the development of slavery in
the subfamily of the Formicinse culminated with the Amazons
of the genus Polyergus, and at the same time it reached its
end, for in this subfamily slavery has not been further developed,
and the representatives of the decay of slavery and its de-
generation to the lowest social parasitism all belong to another
subfamily — the Myrmicinae. In their case, however, no trace
remains among living Fauna of the first half of the process of
development, leading up to the culminating point, and we can
only supply it hypothetically on the analogy of groups 2-4,
which belong to the Formicinae. We may venture to say that
the slave-making instinct possessed by the southern species of
of Strongylognathus is very like that displayed by Polyergus,
and probably passed through similar phylogenetic stages,
such as we can still observe in the mixed colonies of F. san-
guinea and in those of F. truncicola. In this way we may
combine two different parts, so as to form one complete picture,
the materials for one part being derived from the subfamily
of the Formicinae, and those for the other part from the sub-
family of the Myrmicinae, and thus they supplement one another,
and we have a hypothetical history of the slave-making
instinct among ants.
What bearing has this upon what is probably the actual
history of slavery among ants ? It shows that the instinct
appeared in the Formicinae in a geologically much later age than
in the Myrmicinae ; for this is the reason for the absence, in
the case of the Formicinae, of all real evidence bearing upon
the second half of the evolution of slavery, and in the case of
the Myrmicinae of all real evidence bearing upon the first part.
Among the Formicinae we still meet with many progressive and
preparatory grades in the development of the slave-making
414 MODEKN BIOLOGY
instinct, which culminates in Polyergus ; among the Myrmicinae
there are almost exclusively descending grades, so that in this
subfamily the instinct seems to pass from its culminating point
down to complete parasitic degeneration in Anergates.
The instinct prompting ants to steal workers of other
species to be their slaves developed at least twice in the history
of ants, and its appearances occurred in different ages, within
two different subfamilies, and quite independently one of the
other.
But within these two subfamilies the history of the slave-
making instinct is not one single line of evolution, but several
lines, beginning among various genera and species, that
originally led an independent existence ; these lines having
very various development and belonging to different periods.
At the conclusion of the fifth section of our biological
survey, I pointed out that the robber-ants of the Strongylo-
gnathus genus (group 6) are probably not closely connected
with those of the Tomognathus genus (group 7). The slave-
making instinct seems to have developed in the ancestors of
these two genera independently of one another, and later in
the ancestors of the northern genus Tomognathus than in those
of the southern Strongylognaihus. Within the latter genus
we find a uniform evolution, connecting the slave-making
species of the south with the parasitical species of the north.
Nevertheless, we must not assume that our present yellow
scimitar-ant (Sir. testaceus, group 7) is the direct descendant
of its present relatives in Southern Europe (Sir. Huberi, group
6), but rather of an extinct species, which formed the starting-
point for the subsequent evolution of all our present species of
Strongylognafhus ; the southern representatives of this stock
became and are robbers, stealing their slaves, whereas the
northern branch of the same stock has lost the slave-keeping
instinct, and has degenerated into a parasitical condition.
Among the ancestors of Anergates (group 9) the slave-making
instinct probably developed and perished much sooner than
in Strongylognafhus ; for the parasitic A. atratulus, that has
no workers, shows the utmost degradation of the slave-making
instinct, whilst Sir. testaceus is still far removed from it. Even
if the Tertiary ancestors of both these genera were identical,
or very closely connected, we must nevertheless assume that,
THE SLAVE-MAKING INSTINCT 415
in the branch of the stock whence our Anergates is descended,
the slave-making instinct began to develop at an earlier epoch
of the Tertiary period than in the branch which gave rise to
the present genus Strongylognathus.
The American parasitic ants belonging to the genera
Epoecus, SympJieidole, and Epipheidole (group 8) represent
theoretically a stage preceding that complete parasitic degenera-
tion which we find in Europe in Anergates (group 9). But
there is apparently no close connexion between the American
and the European genera, and in all probability neither is
closely connected with the North African genus Wheeleria,
with which Santschi's recent observations in Tunis have made
us fully acquainted.1 It stands in the same sort of relation to
Monomorium as Anergates to Tetramorium, but the Wheeleria
males are normal and have wings, and are not degenerate
creatures such as the pupa-like males of Anergates. In this
way the gap that has hitherto existed in the fauna of the Old
World between Strongylognathus and Anergates is filled up,
but not in the sense that Wheeleria is to be regarded as standing
phylogenetically midway between these two genera. The
striking analogy between Wheeleria and Anergates is due perhaps
only to ' biological convergence,' and the resemblance in their
way of life may be a coincidence. Moreover, Santschi has
recently discovered in Tunis temporarily mixed colonies
belonging to the subfamily of Dolichoderinae, formed by the
intrusion of Bothriomyrmex females into Tapinoma colonies.
This form of symbiosis is very like that which we have con-
sidered in group 2&, as existing between Formica truncicola
and fusca, and between consocians and incerta ; it is, however,
phylogenetically quite independent of the evolution of similar
alliances in the other subfamilies of ants.
The subfamily of Formicinse or Camponotinae was much
later than the subfamily of Myrmicinae in developing its
present genera and species, which are very numerous. This
is proved by the fossil representatives of the two subfamilies,
which have come down to us in amber from the middle of the
Tertiary period. Hence, it is only natural that the Formicinaa
should develop the slave-making instinct later than the
1 See Forel, * Moeurs des fourmis parasites des genres Wheeleria et Bothrio-
myrmex ' (Revue Suisse de Zootogie, XIV, fasc. 1, 1906, pp. 51-69).
416 MODEEN BIOLOGY
Myrmicinae, and this is borne out by facts that we considered
in our biological survey of the various groups. Among the
MyrmicinsB of the present day we find almost exclusively
descending grades of slavery, and among the Formicinse many
preparatory and ascending grades of the slave-making instinct,
leading up to its culminating point.
Let us once more turn our attention to these forms.
The Amazons of the genus Polyergus (group 4) represent
the development of this instinct at the highest point which it
reaches in the subfamily of the Formicinse. Phylogenetically
they may be traced back to the genus Formica, and so they
form one real line of evolution with groups 2 and 3. But by
this expression I do not mean that the genus Polyergus is
directly descended from one of the present species of Formica
belonging to group 3, for instance, from the red robber-ant,
for there is a clear morphological and biological distinction
between Polyergus and the present robber-ants of the
genus Formica (cf. note 2, p. 398). We must therefore
assume the phylogenetic separation of these two genera to
have taken place in some remote past, probably in the second
half of the Tertiary period, when Europe and Asia were not yet
cut off from North America. At that time there was a species
of Formica, resembling our F. sanguinea in its mode of life,
having developed the slave-making instinct in a higher degree
than other species, and this species became the ancestor of
the famous race of Amazons, which exists in several sub-
species, all belonging practically to one single species, in both
hemispheres.
At a later period, when the division between the eastern
and the western continents was going on, but was still not
complete, there arose the red robber-ants (F. sanguinea),
being descended from a race resembling our present F. trunci-
cola both morphologically and biologically. F. sanguinea has
not developed the slave-making instinct so highly as Polyergus,
and this fact suggests that in the former the instinct made
itself felt later ; moreover, the subspecies in both continents
have developed it in different ways, and those in North America
are still behind those in Europe.1
Of still later origin than our present F. sanguinea is F.
1 Cf. group 3 in the biological survey, p. 394.
THE SLAVE-MAKING INSTINCT 417
truncicola, which did not branch off from F. rufa as a distinct
subspecies until North America was quite cut off from Europe
and Asia, that is to say, probably during the Pleistocene
epoch, for it does not occur in North America, although the
species and subspecies of the rufa group are more numerous
and varied there than here. On the other hand, other repre-
sentatives of the same group are found in America, which,
like F. truncicola, form temporarily mixed adoption-colonies
with the workers of other and smaller species of Formica.
The instinct prompting the females of various branches of
the large and ancient rufa group, to found their new colonies
with the help of workers belonging to some other smaller
species of the same genus,1 is the starting-point for the develop-
ment of the slave-making instinct, among the slave-keeping
ants belonging to the genera Formica and Polyergus. But
the adoption-colonies formed at the present day by F. truncicola,
consocians, &c., are only the modern counterparts of similar
adoption-colonies, whence at a much earlier date the robber-
colonies of our present red robber-ants and Amazons originated
phylogenetically.
We see, therefore, that what was probably the real history
of slavery amongst ants breaks up into a number of distinct
processes of evolution, originating at different times and attain-
ing various degrees of completeness. We may compare the
evolution of slavery among ants with a tree, sending out many
boughs and branches from its trunk. The oldest bough,
shooting off near the root, is the genus Anergates ; the blossoms
once borne by its branches have withered long ago, and the
bough itself is dying. The bough with its branches that
represents the genus Polyergus is in full blossom ; it springs from
a higher point halfway up the trunk. Above it we see other,
younger branches, which are the slave-making species of
Formica of the present day. They bear buds showing the
slave-making instinct to be growing, but as yet these buds
are not fully opened. At the top of the tree are some still
younger shoots, on which the buds have only just formed ;
these are the species of Formica living temporarily in mixed
1 I shall return further on to this subject, and give the reason why it is
in the species allied to F. rufa that the females have lost the instinct to found
new colonies independently.
2 E
418 MODERN BIOLOGY
colonies, but stealing no slaves. But will they become real
slave-robbers at some future time ? We can only offer con-
jectures on this subject, for the evolution of species and their
instincts does not depend solely upon the interior laws of
evolution,1 which supply the Anlage or tendency to produce
new forms, but also upon the exterior circumstances of life,
which condition the realisation of this possible evolution, and
co-operate as causes producing it. If the circumstances under
which a species lives are persistent and regular, it is probable
that there will be no change in the species itself and its instincts ;
but if the external conditions of life are altered owing to
climatic and other changes, it is probable that modifications
will ensue in the mode of existence of the species in question,
and in the organs and instincts concerned.
Geology teaches us that in both the Tertiary period and
the Pleistocene epoch great and far-reaching climatic changes
have repeatedly occurred in the northern hemisphere. These
changes could not fail to affect the ants within this region, and
led to modifications in the structure of their nests, in their way
of procuring food, and in all the circumstances of their life.
We shall therefore probably be right in connecting the repeated
origin of and the various degrees in the evolution of the slave-
making instinct among ants, with the different climatic
changes that took place during the Csenozoic age.
To many persons this hypothesis will perhaps seem' very
daring, yet there are good foundations for it in fact. In
discussing the sixth and seventh groups, I was able to show
that our little scimitar-ant, Strongylognafhus testaceus, had
most likely lost the slave-making instinct under the influence
of our northern climate, whilst its southern connexions still
retain it. It is unimportant whether we are to regard this as
a result of the northward migration of an ant, formerly living
in the south, or as a consequence of a gradual diminution in
the summer heat in a locality already occupied by that species.
The decay of the slave-making instinct in a species that once
kept slaves can easily be explained by climatic changes ; but
can the origin of this instinct be accounted for on similar lines
1 With regard to the nature of these laws, which on its material side depends
upon the constitution of the chromatin-substance in the germ-cells, see pp. 176,
&c.
THE SLAVE-MAKING INSTINCT 419
in a species that once had no slaves ? This is the next question
that we have to answer.
We have already seen in speaking of the first and second
groups (pp. 391, &c.) that we must regard, as a preliminary to
the evolution of that instinct, a habit possessed by certain
kinds of ants, of not forming new colonies for themselves, but
the impregnated females after the copulation flight are adopted
in the nests of ants belonging to another species (group 2&).
The existence of this habit proves that the queens have lost
the instinct prompting them to found new and independent
colonies, and, instead of settling down by themselves, they
seek out the workers of another species. What can have
caused such a lack of independence on their part ?
It would be produced most readily in a species that not
only is very abundant, but possesses very populous colonies,
living in huge nests, so that the surrounding district is domin-
ated by the inhabitants of the colony. In such a district the
queens, after their copulation flight, would be sure to meet
workers ready to welcome them, and thus they would be
relieved of the necessity for founding new settlements alone.
These are exactly the circumstances under which live our
northern wood-ant, F. rufa, and its nearest connexions of the
rufa group in Europe, Asia, and North America,1 and they
represent a form of adaptation to life among the forest Flora
of an Arctic climate. The genus Formica has literally a
circumpolar distribution, and the rufa group, that builds high
heaps, predominates more and more, the further north we go.
These huge nests sec.ure to their occupants a high and even
temperature, and so protect them against the severity of the
climate, and render it possible for the young to be reared
even in dense, damp forests. Not only do the decaying
vegetable substances, of which the heaps are constructed, pro-
duce heat, but the heaps are so shaped as to catch the rays
of the sun, and their dry domes are raised well above the damp
earth — and all these are marks of adaptation to life in an
Arctic forest. In this way we can understand how, in the
species belonging to the rufa group, the queens may have
lost the instinct prompting them to found new colonies, and
1 On this subject see the details given under group 2a, p. 391.
2 E 2
420 MODEKN BIOLOGY
this loss would be an indirect consequence of the adaptation of
these ants to life among Arctic forest Flora.
If the instinct was once lost, the descendants of these
ants would be devoid of it, even supposing the species phylo-
genetically descended from these wood-ants to become rarer,
in which case the opportunity would more rarely present
itself for the queens to meet workers of their own species,
and form new colonies by their aid. They would have to
seek a home with some other common species of Formica, and
thus arose the adoption-colonies of F. truncicola, exsecta, &c.,
in Europe, and of other members of the rufa group in North
America. Therefore the formation of these temporarily mixed
adoption-colonies, which represent a preliminary stage leading
to the formation of permanently mixed robber-colonies, is
connected with the adaptation of their ancestors to life in the
Arctic forests. We may even go so far as to pronounce it
probable that, in consequence of a gradual change in the
climatic conditions which had been most suitable to the
genuine wood-ant F. rufa, fresh subspecies branched off from
the original stock, and took up their abode outside the forests,
as is the case with F. truncicola, consocians, &c.
But a further question presents itself : ' How can altered
climatic conditions cause a slave-making instinct to arise in an
ant that at first lived with its assistant ants in only temporarily
mixed colonies ? ' Biological facts give us many indications
that will aid us in answering this question. Let us take as an
instance our F. truncicola, which employs the workers of F.
fusca in founding new colonies. What prevents it from
stealing slaves ? There is no direct reason for its doing so.
Like F. rufa, F. truncicola lives chiefly by keeping aphides,
and does not catch insects, although occasionally it carries
flies and other insects into the nest. It will, however, readily
eat the pupae of other kinds of ants if they are given to it. Let
us now imagine that in some district, occupied by F. truncicola,
climatic changes gradually replaced the northern forest Flora
by that of steppes covered with heather. As aphides gradually
became less abundant on the trees and bushes, the ant would
be forced to live on insects more than it had done previously,
and as it is a large, strong ant, and its colonies, if long estab-
lished, become very populous, it would be able to find food
THE SLAVE-MAKING INSTINCT 421
easily by stealing the pupae of other smaller ants living in
the same region. The commonest of the smaller species of
Formica is F. fusca, and if there are any fusca nests in the
neighbourhood, young truncicola colonies, containing workers
that have been brought up by F. fusca, would rear at least
some of the stolen pupae to be their slaves.1 I have actually
found confirmation of this theory, and as soon as this process
occurs, we have a robber-colony.
Our red robber-ant F. sanguinea is really an ant living on
steppes and moors, and feeding on insects and the stolen
pupae of other ants. It belongs as much to the moors of the
north as F. rufa does to the forests. In F. sanguinea we have
an instance of a regular slave-breeder, stealing and rearing
as slaves the worker-pupae of F. fusca or of F. rufibarbis. But
these are the species of Formica by whose help the females
of sanguinea found their new colonies. Therefore, each
individual colony of this robber-ant is for a time a mixed
adoption-colony, before it becomes permanently a mixed
robber-colony. Are we not justified in believing that the
race has developed in a similar way by passing through a
truncicola stage ?
Apparently one link is still missing in the chain of evidence.
If one individual truncicola colony begins to steal and rear
fusca pupae, and repeats its raids upon the neighbouring
fusca nests every year, it does indeed become a new robber-
colony, but this does not explain how the slave-making in-
stinct has become hereditary in the whole species, as it is in
F. sanguinea.
Let us see why this is so.
We must begin by noticing that by no means all the colonies
of ancestors of sanguinea resembling truncicola adopted the
practice of stealing slaves suddenly and simultaneously.
Some adopted it earlier, and some later, according to their
external circumstances. This is suggested by the fact that at
the present time the North American subspecies of F. san-
guinea have developed the slave-making instinct in a lower
degree than the European variety of the same species. It
would be a mistake therefore to imagine that the ancestors
1 See group 26, p. 392, and also my ' Ursprung und Ent wicklung denSklaverei
bei den Ameisen,' p. 167.
422 MODEKN BIOLOGY
of the red robber-ant suddenly acquired an hereditary instinct
prompting them to make slaves.
The transmission of instincts, like that of bodily qualities,
is effected by means of the germ-plasm. The impregnated
females of sanguinea transmit the slave-making instinct,
not the workers, which do not normally aid in propagating the
species.1 Let us examine closely the changes that must have
taken place in the hereditary plasm of the queens of that
truncicola type, from which our sanguinea is descended.
The females inherited an instinct prompting them to seek
fusca nests, and to unite with the workers in them for the
purpose of founding new colonies. As I showed on p. 417,
their ancestors of the rufa group (2a) had already lost the
power of founding new colonies independently, and therefore
the truncicola queens (group 26), after the copulation flight,
have to wander about until they find admission into a nest
of the commonest ants of another species of Formica, and
these happen to be F. fusca.
A young truncicola queen, forming an adoption-colony
with workers of F. fusca, needs no 'new instinctive Anlage
or disposition ' in her germ-plasm. Nor do we need to assume
the existence of any in order to account for the origin of the
instinct prompting the workers to steal the pupae of other ants,
for truncicola, like other species of the rufa group, lives at any
rate partially on stolen insects, and when impelled by want
of food, it will attack and plunder weak colonies of other
species of ants, especially fusca colonies, as these ants are
remarkable for their cowardice. We need not therefore assume
the existence of any * new instinctive Anlage ' in the germ-plasm
1 I say * normally ' in contrast to parthenogenesis, which, however, in
Formica produces only males. According to observations that I made in
Luxemburg, colonies of F. pratensis having no queens, but existing under
natural conditions, go on for two or three years producing thousands of males,
all being hatched from the unfertilised eggs of the workers. If on the copu-
lation flight these males pair with females from other colonies, a transmission
of the properties of the workers, that produced the males, to the workers of
the next generation is quite possible, through the male germ-plasm. This point
has not hitherto received as much attention as it deserves, although it throws
considerable light upon the difficult problem of the development of instincts
among the workers of the social insects. In some species of Lasius, workers
appear to be produced directly by parthenogenesis. In giving the above
account of the development of the slave-making instinct, I have left partheno-
genesis out of consideration, because under normal circumstances the queens,
not the workers, lay the eggs from which the males also are produced.
HEKEDITAKY INSTINCTS 423
of the truncicola queens, in order to account for the origin of
the plundering instinct in the workers, nor for their habit of
rearing only the fusca pupae from among all those that they
steal ; the workers were themselves reared by fusca, and for
years formed a mixed adoption- colony with the workers of
this species ; for this reason the pupae of fusca workers impress
the individual truncicola ants, through their sense of smell, as
being familiar companions and not strangers.
Here we have all the preliminaries requisite for gradually
producing a definite hereditary instinct for making slaves. The
chromosomes of the impregnated females' germ-cells, which
are the material bearers of heredity, need only favourable com-
bination in order to secure the transmission of the slave-making
instinct. I cannot discover any difficulty as to fixing a
combination of elements already existing. The truncicola
queen already possesses the instinct to unite with fusca workers
in founding her colony, and she may transmit this instinct
to her offspring of the working caste, but in a form adapted
to their character as workers. This would strengthen, in the
robber-ants reared by fusca, an already existing inclination to
ally themselves with workers of that species, and, as soon
as they are aware of a dearth of workers in their colony, they
make expeditions in quest of fusca pupae.
Here we see, fully developed, the hereditary slave-making
instinct of our red robber-ants.
But, it may be asked, what has Darwin's Natural Selection
to do with this evolution of the slave-making instinct ? No
allusion at all has been made to it. Can we not assign to it
at least a subordinate part in the evolution ? Yes, we may
justly assign to it the part of the executioner, as it wipes off
the face of the earth those colonies of ants which have shown
themselves incapable of maintaining existence, and thus it
averts unfavourable variations in the germ-plasm of the
queens. This is, however, the limit of its action, it is not
concerned with either the origin or the further evolution of
slavery. It is an interesting fact that the theory of natural
selection proves to have no more than this to do with the
evolution of the slave-making instinct, which Darwin in the
1 Origin of Species ' considered capable of explanation by means
of natural selection (cf. p. 411).
424 MODERN BIOLOGY
' Nature will not be robbed of her veil of mystery, and
what she refuses to reveal, you will not extort from her by
using screws and levers.' Certainly screws and levers are of
no more avail than unprofitable theoretical speculations.
But much may be learnt by careful observations and experi-
ments, and by cautious deductions from them. Perhaps I have
succeeded in making such use of the newest materials supplied
by biology as to raise, at least in some degree, the veil of mystery
that has hitherto enveloped the history of slavery among ants.
We may hope that, as biological research advances, more
light will gradually be thrown upon the details of the phylo-
genetic evolution of the slave-making instinct. The sketch
given above is only a modest attempt to solve this very
interesting problem. Let us now sum up shortly the results
of our examination of this instinct, and consider its bearing
upon the theory of evolution.
The development of the slave-making instinct is a matter
of hypothesis and not of fact ; but the hypothesis proceeds
directly from the facts, if we compare them carefully with one
another and investigate their genetic connexion. It is a
well-grounded hypothesis, as it supplies us with a uniform
and satisfactory answer to the question how the actually
existent forms of slavery and social parasitism among ants
could have been produced by natural causes.
A close examination of the slave-making instinct has shown
how quite new instincts may arise in animals from simple
foundations, how they may develop to an astonishing point,
and how finally they can degenerate and disappear. If we
fix our attention only upon the culminating point of this
development, e.g. upon the conspicuous degree in which
Polyergus possesses the slave-making instinct, we are inclined
at first to say : ' This instinct must have been implanted in the
Amazon ants at their creation, for they cannot exist without
slaves ; therefore it is impossible for their instinctive desire
to steal slaves to have arisen through evolution.'
My answer to this objection is that it is undoubtedly an
absolute necessity for the genus Polyergus in its present form
to possess the - slave-stealing instinct, as otherwise it would
cease to exist. But if Polyergus is phylogenetically descended
from the genus Formica, which contains other slave-keeping
CONCLUSIONS 425
species not so completely dependent upon their slaves, and
possessing the slave-making instinct in various degrees, it is
possible to give a simple and natural explanation of the origin
of the same instinct in Polyergus, though this ant possesses
it in a far more perfect form. The species have undergone
morphological changes as their instincts have developed ;
and our examination has shown us that the instincts of these
ants supply precisely the biological impetus causing modifica-
tions in their forms, and producing new species and genera.
The development of the slave-making instinct marked off
the red robber-ant (Formica sanguinea) as a species distinct
from another belonging to the same genus, but not yet pos-
sessing this instinct ; and as a result of its further development,
the genus Polyergus, which differs greatly from Formica in the
formation of its mandibles, branched off from a Tertiary species
of Formica. The decay of the slave-making instinct in the
genus Strongylognathus resulted in the production of a new
species Sir. testaceus. The influence of a parasitic existence
has led to the formation of a number of new genera, such as
Wheeleria, Epoecus, Aner gates, &c., which differ widely from
their nearest systematic relations in the form of their males
and females, as well as in having no workers. In short, the
history of the evolution of the slave-making instinct has
afforded us an opportunity of learning, from clear examples,
how new species and genera of animals may come into exist-
ence, as their instincts develop.
12. CONCLUSIONS AND RESULTS
I might bring forward a number of similar instances of
evolution occurring among the inquilines of ants and termites,
and among ants and termites themselves, but they would
all lead to the same conclusion as those already considered.
We cannot avoid accepting the hypothesis of a race-evolution,
both of species and "of their peculiar instincts, but this evolution
is not on the lines of Darwin's hypothesis. This result is
not new. Twenty years ago I wrote a paper on the evolution
of instincts in the primaeval world,1 in which I arrived at the
1 ' Die Entwicklung der Instinkte in der Urwelt ' (Stimmen aus Maria-Laach,
XXVIII, 1885, p. 481).
426 MODEKN BIOLOGY
same conclusion, although not with as much clearness and
certainty as at the present time. No change has taken place
in my opinions on this subject, but they have become more
definite, after twenty years devoted to my special branch
of scientific research.
Let us now once more sum up briefly the results of our
criticism and comparison of the theories of permanence and
descent, with which we have been occupied in this section.
Of the two contrasted theories, the former, which main-
tains the fixity of species, is apparently supported by the great
majority of facts coming immediately under our observation,
because the evolution of many species is complete at the
present time, and that of others advances so slowly as to
be imperceptible. It is therefore only in exceptional cases
that we find species in which we can show evolution to be
still going on. As an instance from my own department,
I was only able to refer to the evolution of Dinarda forms
(pp. 315, &c.), which seems to be still incomplete in two of
the four species, or rather subspecies, belonging to this group.
We are able somewhat more frequently to discover cases
in which the formation of new species has been recent, i.e.
has occurred in the last geological period. I discussed in
detail some of these cases (pp. 348, &c.) which may be regarded
as direct evidence in support of the theory of evolution, and
I considered at some length the change in the habits of the
beetles belonging to the genera Doryloxenus and Pygostenus,
which were at first inquilines among the wandering-ants,
and then found hospitality among the termites. It must
be acknowledged, however, that there is comparatively little
direct evidence in favour of the evolution of species.
Facts which, on the surface, seem to support the theory of
permanence, prove on scientific examination to supply evidence
in favour of the theory of evolution, as soon as we bring com-
parative morphology, biology, and embryology to bear upon
them, even if we disregard palaeontology.
I referred to a number of instances showing that the
systematic peculiarities, distinguishing the species, genera,
and families of inquilines among ants and termites from their
relatives leading an independent (not myrmecophile or ter-
mitophile) existence, are all to be regarded as characteristics
CONCLUSIONS 427
due to adaptation to a myrmecophile or termitophile mode
of life. These characteristics become intelligible only when
we can assign their causes to them, and this necessitates our
admitting that an evolution of the systematic species of the
same stock can take place.
The theory of permanence can offer a satisfactory account
of these characteristics only in as far as it accepts, simply
as existing facts, the very various beneficial morphological
and biological conditions that present themselves, and does
not seek into causes, and demands no explanation beyond
this — ' the various species of inquilines were originally created
in their actual form at the same time as their hosts were
created, and expressly for them.' This explanation may
satisfy one who is a teleologist and nothing more, but not a
scientific student of nature, for his thoughts may, and inevit-
ably must, pass on to the further question : * Is it not possible
to assign to natural causes the origin of these beneficial
adaptations ? ' If he takes his stand on the theory of evolution,
he can answer this question in the affirmative, although he
need not be under any optimistic delusion regarding the
hypothetical character of the various attempts hitherto
made at explanation.
In considering the history of slavery amongst ants, we
found an instance of the evolution of an instinct, which con-
firms the above statement. It appeared that only the theory
of evolution in a modified form enabled us to arrive at a real
comprehension of the origin of these biological conditions.
Let us once more return to our discussion of the doctrine
of evolution. In Chapter IX (pp. 272, &c.) I showed that the
recognition of an evolution of the systematic species belonging
to one stock was closely connected with the Copernican theory
of the universe. The geological evolution of our planet is
intimately related with a biological evolution, which appears
in a succession of various Fauna and Flora, extending from
those which are the objects of paleeontological research, to
those of the present day, and, according to the fundamental
principles of the Christian cosmogony, we are perfectly justified
in admitting that natural causes may explain this succession.
We shall therefore cease to regard the Fauna and Flora of the
present time as fixed in number, distinct from and absolutely
428 MODERN BIOLOGY
independent of their predecessors, to account for whose
existence it was enough to refer to the Creator's almighty
power. On the contrary, we shall consider our present plants
and animals as representing the close of a process of natural
evolution, and we shall try to penetrate into the secrets of the
differentiating methods of nature, which have given rise to
this process. As I have shown in the examples already dis-
cussed, this attempt is by no means a barren and unprofitable
speculation, based on nothing but vague suppositions ; on
the contrary, the final results are in such astonishing agreement
with the hypotheses supplied by the method adopted, that
it is hardly possible to avoid the conclusion that we are now
on the right road towards solving this difficult problem in
nature.
Of two hypotheses in natural science or natural philosophy,
put forward as offering an explanation of one and the same
series of facts, it behoves us always to choose the one which
succeeds in explaining most by natural causes, and on this
principle we can hardly hesitate to choose the theory of descent
in preference to that of permanence.
I trust that I have now made clear the practical importance
of the distinction drawn in Chapter IX (pp. 296, &c.) between
systematic species and natural species. I stated then, that if we
accepted a modified theory of evolution, we must class together
definite series of systematic species, which probably are of
common origin, as forming one natural species, and trace
themTback to one common primitive form. If we wish to
account for the origin of these primitive forms, we must
have recourse to the old doctrine of creation and say : ' The
natural species were originally in their primitive forms produced
by God directly out of matter.' The theory of permanence
maintains that the present systematic species were originally
created in their present form.
I believe therefore that no blow has been struck at the
Christian dogma of the creation by all our preceding discussion
of the theories of permanence and descent with reference
to ants and termites and their inquilines. It is, for instance,
a matter of perfect indifference to the Christian cosmogony
whether each individual systematic species of the Clavigeridae
was directly created, or whether we may include in one natural
CONCLUSIONS 429
species all the systematic genera and species of the Clavigeridae
as well as the genera and species of the subfamily of the
Pselaphidae, so that this one natural species would include
a very large family of beetles, consisting of several hundred
genera and many thousand systematic species.
In the same way it is indifferent to Christian cosmogony
whether we regard the species of the family of Termitoxeniidae
as directly created, or as forming one natural species with the
Muscidae and Phoridae, two families of Diptera.1
The ascertained facts, which I have described, suggest
that the latter course is the more correct, and we may follow
it without any danger of wrecking our faith as Christians.
Indeed, my own conviction is that God's power and wisdom
are shown forth much more clearly by bringing about these ex-
tremely various morphological and biological conditions through
the natural causes of a race-evolution, than they would be by
a direct creation of the various systematic species.
In the sixth edition of his ' Gottesbeweise,' 2 Father von
Hammerstein writes as follows : ' If the Creator did not create I
each single species of animal in its present form, but caused I
it to acquire its present appearance and instincts by means I
of an independent evolution, carried on through a long line
of ancestry, His wisdom and power are manifested the more
clearly. Therefore if the theory of evolution is provecT to
be true within definite limits, it by no means sets aside the
Creator, but, on the contrary, an all-wise and all-powerful
Creator becomes the more necessary and indispensable, as
the First Cause of the evolution of the organic species. A
simile will bring out the truth of this very clearly. A billiard
player wishes to send a hundred balls in particular directions ;
which will require greater skill — to make a hundred strokes
and send each ball separately to its goal, or, by hitting one
ball, to send all the ninety-nine others in the directions which
he has in view ? '
1 I may here repeat what I said before (see p. 297), and state clearly that I
have no intention of defining the whole extent of these natural species, which
may be much greater than I have said.
2 Treves 1903, p. 150.
CHAPTEK XI
THE THEORY OF DESCENT IN ITS APPLICATION TO MAN ]
(Plates VI and VII)
PRELIMINARY OBSERVATIONS.
Great importance of this question (p. 431).
1. Is THERE ANY JUSTIFICATION FOR TAKING A PURELY ZOOLOGICAL VlEW OF
MAN ?
No, for it overlooks the chief point — his intellectual and spiritual life.
For this reason psychology has the best right to judge of the nature
and origin of man (p. 433). A purely zoological view of man is
one-sided and based on false premises (p. 434). Karl E. von Baer
on the materialistic explanation of the intellectual life (p. 435).
Only an act of creation can have produced the human soul (p. 436).
What are we to understand by the creation of man ? St. Augustine
on this subject (p. 437). Philosophical reflections on the idea of
the creation of man (p. 439). The Thomistic doctrine of the
sequence of various forms of being in the individual development of
man. Its application to the theory of descent (p. 440). How far
is zoology competent to judge of the hypothetical phylogeny of
man ? (p. 442)
2. WHAT ACTUAL EVIDENCE is THERE OF THE DESCENT OF MAN FROM
BEASTS ?
(a)- A Glance at the Comparative Morphology of Man and Beasts.
Wiedersheim's « testimony ' to it (p. 443). Skeletons of apes and men.
Rudimentary organs (p. 445).
(b) The Biogenetic Law and its Application to Man.
Haeckel's anthropogeny and the 22 or 30 phylogenetic stages in the
1 Objections have been made in several quarters to my adoption of the
term ' theory of descent ' to designate the theory of the evolution of the
organic species from their original stock. ' Descent ' implies derivation from
some earlier stock, and, according to the theory of evolution, definite series of
systematic species are related through being derived from a common stock,
and the systematic species of the present day are descended from other extinct
species belonging to previous ages, and thus the name ' theory of descent ' seems
to me very suitable. We need not abandon the word, or the idea which it
conveys, because they have been put to a bad use by the Monists. Moreover,
the name ' theory of descent ' has been generally adopted, at least in scientific
circles, to designate the evolution of organisms from an earlier stock. I do
not think that anything would be gained by our carefully avoiding this name,
and substituting for it ' theory of evolution,' ' transformation theory,' or
* adaptation theory.' If we did so, our opponents might reasonably regard
it as a sign of weakness to be afraid of a word, after we had accepted the
thing that it denotes. The particular form of the theory of descent, that I
have shown in the preceding chapters to be acceptable from a scientific point
of view, is not monophyletic but polyphyletic ; nevertheless it does not seem
expedient to reject the word ' theory of descent ' and replace it by ' polyphy-
logeny.' Cf. on this subject the remarks in the preface to this edition.
430
MAN AND THE THEOKY OF DESCENT 431
embryology of man (p. 446). Criticism of the biogenetic law and
its application to man (p. 449). Two classes of theories regarding
the descent of man from beasts (p. 455).
(c) The Theory of direct Relationship between Man and the Higher Apes.
Selenka's evidence in support of it, based on the formation of the
placenta (p. 456). Friedenthal's discovery of ' blood-relationship '
between man and the primates (p. 457). Direct relationship between
man and the higher apes cannot be assumed to exist (p. 461).
(d) The Theory of indirect or remote Relationship, based on the Community of
Origin between Man and Apes.
Klaatsch's theory respecting the common ancestor of both (p. 462).
Palaeontological arguments against this theory (p. 464).
3. CRITICISM OF RECENT PALJEONTOLOGICAL AND PREHISTORIC EVIDENCE
FOR THE DESCENT OF MAN FROM BEASTS.
(a) The Upright Ape-man (Pithecanthropus erectus).
Not to be regarded as a link between ape and man, but as a large,
genuine ape (p. 466).
(6) The Neandertal Man and his Contemporaries.
Uncertainty as to the geological date of his existence (p. 470).
Schwalbe's theory, according to which the Neandertal man and
his contemporaries formed a peculiar intermediate genus or species
(Homo primigenius), standing between apes and men (p. 471).
Macnamara's examination of this theory (p. 471). Kramberger's
recent investigations regarding Homo primigenius (p. 472). He
proves to be merely an early "subspecies of Homo sapiens (p. 473).
Kollmann's theory of pygmies (p. 475).
(c) Conclusions.
Natural science can give us no certain, trustworthy information on
the subject of the descent of man from beasts (p. 476). Haeckel's
pedigree of the primates a mere fiction (p. 476). Professor Branco's
opinion respecting prehistoric man (p. 477). Palaeontology knows
nothing of any ancestors of man (p. 478). Untrust worthiness of
the purely zoological view of man (p. 479).
PRELIMINARY OBSERVATIONS
BEFORE we end our examination of the comparative merits
of the theories of permanence and descent, I must answer
one more question, which has probably occurred to many of
my readers. ' If we give up the fixity of the systematic
species, and substitute for it an evolution of the species within
definite series of forms, each constituting a natural species,
must we not apply the same law of evolution to the highest of
the systematic species, i.e. to Homo sapiens ? ' 1
I do not intend to discuss this point in its dogmatic and
exegetical aspect, but I may make a few remarks that will
throw some light upon it.
The question with which we are now concerned is so im-
portant, and has so vast a bearing upon the highest interests
1 Cf. Chapter IX, p. 296, and X, p. 428.
432 MODERN BIOLOGY
of mankind, that it cannot be dismissed with mere cut-and-
dry phrases. I should describe as a phrase of this kind the
statement which the materialists generally make in support
of the descent of man from beasts : viz. that zoologically
his descent from beasts is self-evident !
st this statement I may say :
(1) It rests on the tacit assumption that zoology is the
I " only science entitled to judge of the origin ofjtnan.
(2J It rests further on the tacit assumption that the descent
2- — of man from beasts has already been actually proved by
means ot zoology.
"""We cannot, however, tolerate tacit assumptions on a
subject of such gravity and having such important conse-
quences. Therefore, we must examine it critically, and find
answers for the two following questions : (1) Is zoology really
the only science entitled to form an opinion regarding the
origin of man ? (2) What actual evidence is supplied by
zoology in support of the descent of man from beasts ?
1. Is THEBB ANY JUSTIFICATION FOR TAKING A PURELY
ZOOLOGICAL VIEW OF MAN ?
If man at the present day were actually nothing more than
a higher animal, — if .there were no essential difference between
man and beast, it would, perhaps, be an obvious answer to
give, when asked whether man is descended from beasts : ' He
must have come from a Tertiary mammal, as he could not
have come into being otherwise.' This answer would not be
quite scientific, for it would not be supported by evidence
derived from facts, but it would at all events be psychologically
near the truth. In fact, this answer, which for the sake of
brevity I will call the purely zoological answer, would be given
without hesitation by all those who regard the zoological
aspect of the question as the only one worth consideration.
Unhappily I am forced to admit that not a few of our modern
zoologists seem to assume zoology to be our sole source of
information regarding the nature and origin of man.1 For
this reason they reject the results of other sciences, if they do
1 For a criticism of this view see also J. Grasset, Les limites de la biologic,
Paris, 1902.
SCIENCES DEALING WITH MAN 4B3
not agree with this assumption. But it is based upon a very
one-sided opinion, and it would be most desirable if, in this
case, we had somewhat more of that freedom from bias of
which we hear so much. Although I am myself a zoologist,
and esteem zoology and its scientific adherents very highly, I
feel inclined to compare a zoologist, who judges man from
a purely zoological point of view, with a printer's apprentice,
who judges of the nature and origin of one of Mozart's com-
positions merely as so much printers' ink.
But what other sciences, besides zoology, have any claim
to be heard on the subject of the nature and origin of man ?
Quite apart from theology, there is above all philosophy,
and especially psychology, the branch of philosophy which
deals with the spiritual life of man. It teaches us to observe
our own spiritual activities, and, by a process of logical deduc-
tion, it traces them back to an immaterial and simple principle
that we call the rational soul of man. It teaches us to compare
our own spiritual life with the manifestations of the animal
soul, that is limited to matters of sense, and thus to recognise
the great difference between man and beasts. A brute has no
power of intellectual abstraction, and therefore it has no
free will, and it cannot manifest what it does not possess. It
cannot express its perceptions and feelings rationally by
means of language ; and, having no reason, it is impossible
for it to possess any science, religion or morality. Man alone
possesses a sensitive and spiritual soul essentially different
from the merely sensitive animal soul.1
It is very easy simply to deny the existence of this distinction
between man and beast, as unhappily superficial thinkers
often do at the present time ; but such a denial can only be
based upon the annihilation of psychology as an independent
science, for the purely zoological method is assumed to be the
only form of comparative psychology for which any justification
exists. Such thinkers concentrate their attention upon the
points common to men and beasts, and try to account for all
the differences between them by asserting that each point of
difference must have been gradually evolved from what was
1 On this subject see my earlier writings : Instinkt und Intelligenz im
Tierreich, Freiburg, 1905, and Vergleichende Studien uber das Seelenleben der
Ameisen und der hoheren Tiere, Freiburg, 1900 ; also Menschen- und Tierseele,
Cologne, 1906.
2 F
434 MODEEN BIOLOGY
at first purely animal, as otherwise it could not exist at all.
Here we have what I have called the one-sided view of the
compositor's apprentice betraying itself again. It is tacitly
taken for granted that the zoological view of man is the only
possible one — and on this false assumption is based a very
common opinion regarding human psychology.
For those who take the purely zoological view, human
religion and morality exist only in as far as they have deve-
loped naturally from animal origins. Everything beyond
this is designated ' mythical,' ' childish,' ' savouring of intellec-
tual slavery,' &c. Of course, the objective element in every
religion disappears, and with it all higher motives for human
morality. There can be no mention of dogmas, with the
exception, of course, of purely zoological dogmas, such as the
biogenetic law. Belief in a personal God and Creator seems
completely overthrown, and the mere suggestion that the
existence of a personal Creator, superior to the universe, may
be proved from zoological facts is rejected with indignation,
as bringing in a metaphysical element that would destroy
the * purity ' of zoology.
Here again we encounter a lamentable one-sidedness in
dealing with the subject.
One who thinks simply as a zoologist is either an agnostic,
denying the power of thought to go beyond the limits of what
zoology teaches, — and in that case he condemns himself to
this intellectual limitation and fetters his own reason ; or he
is a monist, venturing beyond these bounds and asserting that
the monos has in man attained the highest form of animal
existence, — and in that case he has ceased to think purely
zoologically, and is combining zoology and metaphysics, no
less than those do who from zoological facts prove the existence
of a personal Creator superior to the universe. The whole
difference between them is that the theist arrives at a correct,
and the monist at a false, conclusion. Neither the agnostic
nor the monist can rightly claim to possess scientific freedom
from prejudice.
We may once for all dismiss the purely zoological view of
man. I have dwelt upon it at such length only because I
wished to show that it is unworthy of a thoughtful human
being. It is quite evident what opinion we ought to form of
PERCEPTION OF WHAT IS SPIRITUAL 435
all the specious statements, made in academic lecture rooms
and in periodicals dealing with popular science, and professing
to adduce zoological evidence of the descent of man from
beasts. They supply no real evidence at all, being too purely
zoological, and treating man not as what he is, but as what
he ought to be, according to the purely zoological theory,
namely an animal, and nothing more. I wish, however, to
rise to a higher level, and to consider not only the animal,
but also the spiritual side of man. Man's spiritual soul is
essentially different from a brute soul, and can therefore never
have proceeded from it by any natural evolution.1 The
soul of a child requires the powers of the senses to be developed
before its mental powers, but nevertheless it is essentially
different from the soul of a brute, for otherwise the child could
no more be'come a reasonable being than a young ape could.
Karl Ernst von Baer, who is undoubtedly one of the
greatest and most thoughtful students of nature in modern
times, has made use of some similes which describe the materi-
alists' inability tpunderstand what is meant by spiritual.2
{jome one hears a horn, and perhaps recalls the tune, but
naturally does not believe that it is playing itself. Then a
mite, sitting in the horn when it began to blow, exclaims :
' Tune ! nonsense ! I felt it, it was a horrible hurricane that
swept me out of the horn.' But a spider on the outside of
the horn declares that there has been neither music nor
hurricane, merely vibrations, at one moment rapid, at another
slow. The mite and the spider are both right from their
respective points of view, but neither understands music.
Again, let us imagine that a traveller in Central Africa
loses a musical score. A savage looks at it, and takes it for a ' •
bundle' of leaves ; a Hottentot, who has been in contact with 2 ,
Europeans, recognises it as paper ; a European colonist sees 3,
that it has to do with music ; but only a trained musician -
perceives that it is Mozart's Overture to the Zauberflote or
one of Beethoven's Symphonies.
' It is the same thing,' remarks Baer, ' with perception of
what is spiritual. If a man has no tendency to recognise it,
1 Cf. Chapter IX, pp. 283, &c.
2 The following expressions used by von Baer were collected by Stolzle,
K. E. von Baer und seine Weltanschauung, Ratisbon, 1897, pp. 342, 343.
2 F 2
436
MODEKN BIOLOGY
and no appreciation of it, he can leave it alone, only he must
not express an opinion upon it, but be contented with his own
personal consciousness. The student of nature is to a certain
extent justified in stopping short at the point where what is
spiritual begins, because his own observations cease to carry
him further, and he has nothing that he can measure, or
weigh, or perceive, by means of the senses. He has, however,
no right to say that nothing exists, because he cannot see it
or measure it, nor that only what has a body and can be
measured has a real existence, and that what is called spiritual
is only a property or attribute of the body, proceeding from
it. Whoever should speak thus would be like the Hottentot,
seeing lines and dots, but knowing nothing of music, or like
the spider counting, if it could, the vibrations of the horn,
but not hearing the melody.'
I should like to commend these words of Ernst von Baer
to the consideration of all those who, with L. Biichner, Ernst
Haeckel, August Forel, and other materialists, declare the
spiritual side of the human soul to be a mere matter of the
imagination, because it rises above their one-sided view of
the processes of nature.
Because the soul of man is spiritual, it differs from the
brute soul essentially and not merely in degree, and therefore
it can exist only as a result of creation, not of evolution. Even
so prominent an upholder of Darwin's theory of evolution as
A. E. Wallace has acknowledged that the spiritual side of
man cannot have been evolved from animals.1 As soul and
body together constitute one being, man in his completeness
occupies a unique position in nature. Therefore, with regard
to philosophy, there can be no objection to our postulating an
act of creation, in order to account for the origin of man.
Man is man only in virtue of possessing a spiritual soul, and
so the creation of the first man took place when his spiritual
soul was created and united with his body of clay. That God
could make use of matter previously prepared for such a union
by natural causes, so as to form a new being when the union
with the soul was effected, we may assume to be possible. The
dogmatic exegetical question as to how the words of Holy
1 Darwinism : An Exposition of the Theory of Natural Selection, with some of
its applications, London, 1889, Chapter 15, pp. 474, &c.
CKEATION OF MAN 437
Scripture are actually to be interpreted has nothing to do with
this subject, and in this biological study we cannot enter upon
a more detailed discussion of it.1
Our atheistical opponents often taunt us with imagining
the God of the Biblical account of the creation as a sort of
1 potter in human form/ fashioning for Adam a body of clay, and
then breathing the soul into his face. This anthropomorphic \
view of God was described as nimium puerilis cogitatio by St. \
Augustine,2 and it is not shared even by those who are convinced i
1 By far the greater number of theologians believe that the substance which
God employed, when creating man, to unite with a spiritual soul consisted
of inorganic matter. As the creation of man is primarily a dogma of faith,
theologians^ are justified in clingingto the literal interpretation of the text
according to constant tradition ana ihe stale wen ts of the ordinary teaching
authority of the Church (see p. 442, note 1), until satisfactory proof is_given
thajb the text ought- to bp. interpreted otherwise? Natural science is not_yet
in apoSitio'h tgjsupplv such a proof, as will be shown in the second partTof this
chapter? ThlTteaching authority of the Church has not determined how we are
to understand the details of the Biblical account of the creation of man. We
may therefore apply to this difficulty the golden rule laid down by St. Augustine,
who says : ' Et in rebus obscuris atque a nostris oculis remotissimis, si qua
inde scripta etiam divina legerimus, quae possunt salva fide qua imbuimur
alias atque alias parere sententias, in nullam earum nos praecipiti affirmatione
ita proiiciamus, ut si forte diligentius discussa veritas earn recte labefactaverit,
corruamus ; non pro sententia divinarum Scripturarum, sed pro nostra ita
dimicantes, ut earn velimus Scripturarum esse, quae nostra est ; cum potius
earn quae Scripturarum est, nostram esse velle debeamus ' (De Genesi ad
literam, 1. 1, c. 18 ; cf. also ibid. c. 19 and c. 21 ; Migne, Pair, lot., xxxiv,
260-262).
2 I am indebted to Father J. Knabenbauer, S.J., for having drawn my
attention to this passage, which occurs in De Genesi ad literam, 1. 6, c. 11, 12
(Migne, Patr. lat., xxxiv, 347-348). The following quotations also have some
bearing upon this subject. In chapter 11 (' Opera creationis die sexto quomodo
et iam consummata et adhuc inchoata ') : ' Proinde formavit Deus hominem
pulverem terrae, vel limum terrae, hoc est de pulvere vel limo terrae ; et in-
spiravit sive insufflavit in eius faciem spiritum vitae, et factus est homo in
animam vivam. Non tune praedestinatus ; hoc enim ante saeculum in prae-
scientia creatoris : neque tune causaliter vel consummate inchoatus, vel
inchoate consummatus ; hoc enim a saeculo in rationibus primordialibus,
cum simul omnia crearentur ; sed creatus in tempore suo, visibiliter in corpore,
invisibiliter in anima, constans ex anima et corpore.' According to St.
Augustine therefore the material of the human body had been created with
the other elements at the beginning of creation. But how did this material
become a human body ? On this subject St. Augustine says in chapter 12
('Corpus hominis an singulari modo a Deo formatum ') : 'Iam ergo videamus,
quomodo eum fecerit Deus, primum de terra corpus eius ; post etiam de anima
videbimus, si quid valebimus. Quod enim manibus corporalibus Deus de
limp finxerit hominem. nimium puerilis cogitatio est, ita ut si hoc Scriptura
dixisset, magis eum qui scnpsrt translate verbo usum credere deberemus,
quam Deum talibus membrorum lineamentis determinatum qualia videmus
in corporibus nostris. . . . Nee illud audiendum est, quod nonnulli putant, ideo
praecipuum Dei opus esse hominem, quia cetera dixit et facta sunt, hunc autem
ipse fecit : sed ideo potius, quia hunc ad imaginem suam fecit. . . . Non
igitur hoc in honorem hominis deputetur, velut cetera Deus dixerit et facta
sint, hunc autem ipse fecerit ; aut verbo cetera, hunc autem manibus fecerit.
438 MODEBN BIOLOGY
that the Biblical account of the creation is to be understood
literally and not figuratively. The Church has not expressed
any final opinion as to the nature of the substance used by
God in creating the first man, but we may be sure that the
Biblical account of the creation was not intended to give us
information regarding the origin of man from the point of
view of natural science.1
Sed hoc excellit in homine, quia Deus ad imaginem suam hominem fecit,
propter hoc quod ei dedit mentem intellectualem, qua praestat pecoribus.' A
few lines further on St. Augustine repeats himself and says : ' Nee dicendum
est hominem ipse fecit, pecora vero iussit, et facta sunt : et hunc enim et ilia
per verbum suum fecit, per quod facta sunt omnia (lo. i. 5). Sed quia idem
verbum et sapientia et virtus eius est, dicitur et manus eius, non visibile
membrum, sed efficiendi potentia. Nam haec eadem Scriptura, quae dicit
quod Deus hominem de limo terrae finxerit, dicit etiam quod bestias agri de
terra finxerit, quando eas cum volatilibus coeli ad Adam adduxit, ut videret
quid ea vocaret. Sic enim scriptum est : et finxit Deus adhuc de terra omnes
bestias (Gen. i. 25). Si ergo et hominem de terra et bestias de terra ipse
formavit, quid habet homo excellentius in hac re, nisi quod ipse ad imaginem
Dei creatus est ? Nee tamen hoc secundum corpus, sed secundum intellectum
mentis, de quo post loquemur.' Hence follows the conclusion. ' Primus
homo, non aliter quam primordiales causae haberent, formatus fuit.' Cf.
De Oenesi ad literam, 1. 6, c. 15 ; Migne, xxxiv, 349, 350. St. Augustine
is, of course, not thinking of an evolution of the human body in the sense
of the modern theory of descent, and I need not dwell upon this point. There
seems to be two chief ideas in his mind : (1) The difference in God's manner
of creating man and beasts lies principally in the fact that to man He gave
an intelligent soul. (2) By means of primordiales causae the body of man, like
that of every other living creature, was based on rationes seminales. The
holy doctor does not decide how far the causae primordiales and seminales
Rationes effected the preparation of its material. He does not discuss the
nature of the material to which God united the human soul, but says simply :
I f superflue quaeritur, unde hominis corpus Deus fecerit ' (De Genesi contra
^JManich. 1. 2, c. 7 ; Migne, Pair, lat., xxxiv,, 200). He devotes twenty-seven
chapters, however (De Genesi ad literam, 1. 7 ; Migne, xxxiv, 355-371), to
the subject of the nature and origin of the human soul, and rightly insists
upon man's possession of a spiritual soul as being the chief point of difference
between man and beast. Every attempt to separate man absolutely from
beasts with regard to his bdciy"][bram"deVelopment, upright Walk, &c7)Tor to
ralBe hllll, as Bumullef does, to a special position as a branch of the animal
kingdom, is doomed to failure, because it substitutes the accidental for the
essential. All bodily differences between man and beasts are ultimately
due to the fact that the' human body is united with a rational soul. For tEis
animal rationale, towers above tne whole animal kingdom,
whilst in body he represents the highest class of mammal. Cf. my discussion
of Bumuller's work Mensch oder Affe ? in Natur und Offenbarung, XL VIII,
1902, pp. 122-126 ; see also my little work, Menschen- und Tierseele, Cologne,
1906.
1 As I have already shown, the question of the origin of man is of a mixed
character, and revelation and natural science are both concerned with its
solution. It is most important to keep the various aspects of the question
quite distinct, and not to confuse them. On this subject I may quote the
following beautiful and weighty passage from Leo XIII's encyclical * Provi-
dentissimus Deus,' November 18, 1893 :
* Nulla quidem theologum inter et physicum vera dissensio inter cesser it, dum
suis uterque finibus se contineant, id caventes secundum S. Augustini monitum
CBEATION OF MAN 439
From a purely philosophical point of view we cannot contri-
bute much towards the solution of this problem. It is certainly
not an indispensable part of the idea of the creation to believe
that man as a whole was created directly by God, through an
extraordinary interference with the laws of nature ; body and
soul may have been created by God in different ways, the
former indirectly, the latter directly. All that is essential to
the idea of the creation of the human body is that the atoms
composing it should have been originally created by God, and
that the laws governing the formation of the body from those
atoms should also have been imposed upon matter by God's
almighty power. We may still say of every human being
that he is ' God's creature ' both in soul and body, although
only his soul is directly created, whereas his body is produced
from his parents' germ-cells according to the laws of naturajl
growth.
ff* If we apply this consideration to the creation of the first
man, we are confronted with two possibilities. We may
regard it as seemly to assume that God created the whole man
in full perfection, making use, it is true, of already existing
atoms to compose the human body, but creating the spiritual
soul, the chief part of man. To others, however, it may seem
more fitting to believe that in producing the first man, as in
" ne aliquid temere et incognitum pro cognito asserant." Sin tamen dis-
senserint, quemadmodum se gerat theologus, summatim est regula ab eodem
oblata: "Quidquid," inquit, "ipsi de natura rerum veracibus documentis de-
monstrare potuerint, ostendamus nostris Literis non esse contrarium ; quidquid
autem de quibuslibet suis voluminibus his nostris Literis, id est catholicae
fidei, contrarium protulerint, aut aliqua etiam facilitate ostendamus, aut
nulla dubitatione credamus esse falsissimum." De cuius aequitate regulae
in consideratione sit primum, scriptores sacros, seu verius " Spiritum Dei,
qui per ipsos loquebatur, noluisse ista (videl. intimam aspectabilium rerum
constitutionem) docere homines, nulli saluti profutura " ; quare eos, potius
quam explorationem naturae recta prosequantur, res ipsas aliquando describere
et tractare aut quodam translationis modo, aut sicut communis sermo per
ea ferebat tempora, hodieque de multis fert rebus in quotidiana vita, ipsos
inter homines scientissimos. Vulgari autem sermone quum ea primo pro-
prieque efiferantur quae cadunt sub sensus, non dissimiliter scriptor sacer
(monuitque et Doctor Angelicus) "ea secutus est, quae sensibiliter apparent,"
seu quae Deus ipse, homines alloquens, ad eorum captum significavit humano
more.'
H*" It follows from these words of Leo XIII that natural science is left per-
fectly free to investigate the origin of man. If science remains within its
proper limits, its results can never come into real conflict with revelation.
On this subject see Chr. Pesch, De inspiratione S. Scripturae, Freiburg i. B.,
]906, pp. 409, &c. ; Dr. N. Peters, Bibel und Naturwissenschaft, Paderborn,
1906, pp. 11, &c, 36, &c., 42, &c.
440 MODEEN BIOLOGY
producing all other creatures, God employed natural causes
as far as they were capable of co-operating towards this aim.
The quotations from St. Augustine's * De Genesi ad literam '
(p. 437) may, perhaps, be interpreted in this sense although
it would not be easy to grasp the full meaning of his words.
Whilst I am dealing with this subject, I may refer also to
the opinion of St. Thomas Aquinas l regarding the succession
of substantial forms of being in the ontogeny of man, and this
from the purely philosophical standpoint, to some extent
reveals a possibility of accepting a preformation of the first
human body by way of evolution. At the first stage of em-
bryonic development the human embryo would possess a
merely vegetative soul, at the second stage an animal (vegeta-
tive and sensitive) soul, and not until the third stage was
reached would a rational or spiritual soul be created and be
1 Cf. St. Thomas, Summa theol 1, q. 118, a. 2, ad 2 ; Contra gentes, 1. 2,
c. 89 ; De potent, q. 3, a. 9. As one of my critics has actually interpreted the
first of these passages (Summa theol. 1, q. 118, a. 2) in a sense opposed to the
idea of a succession of forms of being, it may be well to give an outline of
the contents of this quaestio. The question raised by St. Thomas is : ' utrum
anima intellectiva causetur e semine.' He mentions various reasons in favour
of this opinion, but decides against it, and states the view of those who assume
that there have been several different forms of being in the development of
man (ad 2). He then declares himself clearly and definitely in favour of the
succession of such forms, but agains£ their simultaneous existence :
' Et ideo dicendum est, quod anima prceexistit in embryone, a principio quidem
nutritiva, postmodum autem sensitiva, et tandem intellectiva. Dicunt ergo
quidam, quod supra animam vegetabilem, quae primo inerat, supervenit
alia anima, quae est sensitiva ; supra illam iterum alia quae est intellectiva.
Et sic sunt in nomine tres animae, quarum una est in potentia ad aliam ;
quod supra improbatum est q. 76, 3. Et ideo alii dicunt, quod ilia eadem
anima, quae primo fuit vegetativa tantum, postmodum per actionem virtutis
quae est in semine, perducitur ad hoc, ut ipsa eadem fiat sensitiva, et tandem
ad hoc, ut ipsa eadem fiat intellectiva, non quidem per virtutem activam
seminis, sed per virtutem superioris agentis, scilicet Dei de foris illustrantis.
. . . Sed hoc stare non potest.'
After giving his reasons for regarding the latter view as untenable, St.
Thomas concludes thus : ' Et ideo dicendum est, quod cum generatio unius
semper sit corruptio alterius, necesse est dicere, quod tarn in homine quam
in animalibus aliis, quando perfectior forma advenit, fit corruptio prioris ; ita
tamen, quod sequens forma habet quidquid habebat prima, et adhuc amplius ;
et sic per multas generationes et corruptiones pervenitur ad ultimam formam
substantialem tarn in homine quam in aliis animalibus.' According to the
opinion here expressed by St. Thomas, there is in the ontogeny of man (and
of beasts) a succession of different forms of being, gradually becoming more
perfect, the lower form always ceasing ex ipso to exist, as soon as the higher
succeeds. It was this thought which I took as the foundation for my com-
parison with the development of the race. Of course St. Thomas had no
idea of such a comparison, for it lies quite outside the range of thought of the
mediaeval theologians. For this reason, in speaking of the creation of the
human soul, St. Thomas adopts the view that the body and soul of the first
man were created simultaneously (Summa theol. 1, q. 90, a. 4).
CREATION OF MAN 441
substituted for the previous forms, which had prepared matter
for its union with the rational soul. It is true that at the
present time many theologians have abandoned this Thomistic
view, and prefer to believe that the rational soul is created
at the moment of conception ; but as this succession of forms
in the development of the individual is by no means incom- £***•*•
patible with the subsequent infusion of the rational soul, ^££J
there would not necessarily be any contradiction involved, if a
hypothetical evolution from a parent stock were assumed to
have taken place in the case of the human body likewise.
We must therefore admit that it would be possible for
anyone to account for the origin of the human body by assum-
ing God to have created a primitive cell, and to say that the
earliest ancestors of man were organisms living as simple
cells ; later on, as the organs were differentiated, and a nervous
system was formed, and a sensitive soul came into existence,
they developed into animals. The organism gradually in-
creased in perfection, and, as the brain developed, this soul in
course of time prepared a human body, suited to be the dwelling
of a rational soul and, through possessing highly developed
brain-centres, able to satisfy the conditions of spiritual activity
and its verbal expression. Assuming this theory to be true,
we may still say that man certainly only became man at the
moment of the creation of his rational soul ; in the previous
stages it would, however, be wrong to say that he was simply
a plant or simply an animal, — he was already a man in process
of development ; and thus in the hypothetical development
of the race there would be a process analogous to that which
we recognise in the ontogeny of the individual, the final form
is the true forma specified, which determines once for all the
character of the whole cycle of development. According to
this theory, the whole development of man occurred within
one and the same natural species, viz. ' man,' l although scientific
systematics may be obliged to classify the ancestors of man as
distinct systematic species, genera, &c. I assign nothing more
1 This manner of accounting for the origin of the human body through
the action of the laws of organic development preserves man's dignity at
least as well as the assumption that he was directly formed of inorganic matter.
Any objection to the theory on this score may be met by a reminder that
man's body even now is produced by germinal development from a fertilised
442 MODERN BIOLOGY
than a purely speculative importance to these suggestions, for
there is an enormous difference between theoretical possibility
and actual reality. Hitherto we have dealt only with the
philosophical principles underlying the former ; in the second
part of this chapter we shall have to discuss the latter.
Let us now sum up shortly the results of the first part of
our investigation into the origin of man.
Zoology, regarding man only from the point of view of
his body, rightly describes him as the highest representative
of the class of mammals, and this is true of his embryonic
development also, which resembles that of other mammals.
He is higher than the other mammals in the material equipment
for the life of the soul, inasmuch as his brain is more perfectly
organised and more highly developed. Thus far zoology and
comparative nervous physiology are competent to judge of man,
and philosophy may even admit that it is not impossible for
the human body to have come into existence in the way
indicated by the theory of evolution. Zoology and its attend-
ant sciences are not, however, competent to judge of the nature
and origin of the human spiritual life, because it is quite
beyond their scope. Hence it follows that zoology cannot
pronounce upon the phylogenetic evolution of man as a whole.
It is limited to the somatic aspect of the question, and even
here it cannot express a final opinion, because body and soul
are united to form one man. The question of the origin of man
is therefore of a mixed character ; l and psychology, which
takes into account his higher part, is best qualified to answer
it ; zoology and its attendant sciences are of suEordinate im-
portance, as they can judge only of his lower part. Psycho-
logy tells us that the higher part of man cannot be of animal
origin, therefore all that is lett ior zoology and its attendant
1 After what has been said above, it is scarcely necessary for me to draw
attention to the fact that the question is of a mixed character also for another
reason : — because not only the natural sciences but theology is concerned
with it, since the creation of man touches a dogma of faith. Dogmatic and
exegetical theologians are therefore fully justified in using much caution and
reserve when they speak of the theory of descent, as they have to take into
consideration both the obvious meaning of the story of creation, and decisions
such as that of the provincial council at Cologne in 1860 (tit. IV, c. 14). A
zoologist, botanist or chemist, who knows nothing of theology, is certainly no
more qualified to express an opinion on matters of faith, than a theologian
would be, knowing nothing of natural science, to discuss the evolution of
Ammonites or Paussidae.
MORPHOLOGY OF MAN AND BEASTS 443
sciences is to answer the question of inferior importance :
' Must we nevertheless believe that the lower part of man is
of animal origin ? '
2. WHAT ACTUAL EVIDENCE is THERE OF THE DESCENT OF
MAN FROM BEASTS ?
(Plates VI and VII)
In discussing the theory of evolution in Chapter IX. I was
careful to point out that the question how far we may
regard the theory of evolution to be based upon facts has
nothing to do with mere a priori possibilities, but means this :
' How far do facts furnish us with actual evidence in support
of an evolution of the race ? ' We are confronted with this
question : ' What actual evidence have we at the present time
to show that man in respect of his body is descended from
animal ancestors ? ' And the answer is this : ' The evidence
is by no means clear and irrefutable, but in many ways it is
obscure and contradictory.'
(a) A Glance at the Comparative Morphology of Man
and Beasts
We are all familiar with the methods of Haeckel, Wieders-
heim, and other upholders of Darwinism, who emphasise in an
exaggerated and often quite misleading manner the well-known
points of resemblance between man and the higher animals
with respect to their bodies, and pass over the divergencies.1
' The structure of man as testimony to his past,' as described
by Wiedersheim in 1887 and even in 1902 (when the third
edition of his work appeared), would be a very weighty
argument in support of the descent of man from beasts, if it
did not contain so many one-sided and distorted statements ;
such writing unfortunately is characteristic of the Darwinian
style of argument, using the name in its worst sense. If we
1 With regard to the points of difference between men and apes, see J.
Bumiiller's little work, Mensch oder Affe, Ravensburg, 1900. Zoological
reasons prevent me from accepting the author's opinion that, with respect to his
body, man forms a distinct group in the animal kingdom. Cf. Natur und
Offenbarung, 1902, pp. 122-126.
444 MODEEN BIOLOGY
believed Wiedersheim, we should regard man of the present
day as a mosaic, patched up of pieces resembling parts of
animals, ancTof rudimentary organs, which he is supposed
to have inherited from his noble ancestors. There is scarcely
an organ in the human body, which Wiedersheim from his
standpoint has not tried to use as testimony to the descent
of man from beasts. Like Haeckel, he even depicts the
prehuman forerunner of man in most minute details. He
knows what his hairy covering was like, how the muscles
of his skin were constructed, and how large the movable
muscles of his ears were ; he knows that the eyes did not look
straight forward, but were set sideways in the head, and that
as compensation for this disadvantage, there was a third eye
in the upper part of the head, which eye we now call the pineal
gland. He has measured the length of the prehuman intestine
and found it to be considerably longer than ours, because it
served to digest nothing but a vegetable diet. He has traced
the development of his protege, and seen how he ceased to be
a vegetarian and adopted a mixed diet, and procured a greater
number of incisors and projecting canine teeth, thus transform-
ing himself into a beast of prey, whilst his intestine grew corre-
spondingly shorter. Before the hand of this primitive man
could wield the stone axe, his teeth were his weapons, and his
huge canine teeth projected like tusks. At the same time
new formations developed on the larynx of our worthy ancestor,
so that his voice acquired power and compass, and became
a means of scaring away his enemies.
Wiedersheimjiescribes our, or rather his, forefathers thus
feature by feature, and presents us with a picture not in any
way scientific, but absolutely imaginary. If we subject all
his ' testimonies ' collectively to serious criticism, none of
them prove genuine. This was shown conclusively by Hamann l
in his review of Wiedersheim's compilation, and G. Eanke,
in his excellent work ' Der Mensch,' has carefully examined
the alleged theromorphic forms of man, and has proved that,
wherever they are not purely imaginary, they are to be regarded
as formations due to arrest in the typical human development,
We need not waste time with any further discussion of the
1 Entwicklungslehre und Darwinismus, 1892, pp. 108, &c.
MOEPHOLOGY OP MAN AND APES 445
fanciful dreams of Wiedersheim and Haeckel, which have
brought the zoological study of man into disrepute.
That there are many morphological resemblances between
man and the higher mammals, and especially the higher apes,
is an undeniable fact, that cannot be disputed. These resem-
blances afford a certain amount of zoological evidence showing
that probably man is, in respect of his body, connected with.
the othermammals, butjthe evidence does not go beyond
a probability. The differences between them are so great
as not to admit of our coming to any definite conclusion on
the phylogenetic question, and they extend to the funda-
mental structure of the skeleton. In comparing the thigh-
bones of man and of the higher apes, 0. Walkhoff l comes to
the following conclusion : ' The radical difference goes so far
as that it is possible to determine analytically from any X-ray
photograph of a frontal section, and even from any complete
piece of bone, whether it belonged to a man or to an ape ;
in other words, whether its owner walked upright or not.'
The reader is requested to refer to Plate VI at the end of the
book, and to compare the human skeleton with that of an
orang utang (Simia satyrus), one of the highest apes. The
great differences in the formation of the trunk and extremities
are at once apparent, and there is no need to point them out.2
Plate VII shows the crania of man and ape respectively,
and the difference between them is enormous. In the ape's
skull the animal element is unmistakable, the face occupies
a very large part of the head, whereas in man it is smaller, as
in man the brain, the instrument of his spiritual life, is of
greater importance than the jaws. A glance at Plates VI and
VII will do more than pages of description to make the reader
realise the differences, which cannot be got rid of by mere
speculations and monistic postulates.
A conscientious zoologist will proceed with great caution
in dealing with the so-called rudimentary organs, which are
1 Studien uber die Entwicklungsmechanik des Primatenshelettes, No. 1 ;
' Das Femur des Menschen und der Anthropomorphen in seiner funktionellen
Gestaltung ' (Biolog. Zentralblatt, 1905, No. 6, pp. 182, &c., esp. p. 184). See
also J. Bumiiller, Das menschliche Femur nebst Beitragen zur Kenntnis der
Affenfemora, Augsburg, 1899, p. 132.
2 For a detailed account of these differences, see J. Ranke, Der Mensch,
I, 437-444, and II, 3, &c., 203, &c.
446 MODEBN BIOLOGY
supposed to afford conclusive evidence of man's descent
from brutes. Many organs were at one time regarded as
useless and rudimentary, because no one had yet discovered
wninr"pnrpose^ they served, T^'or instance, the thymus and
thyroid glands are now no longer reckoned as rudimentary
organs, since investigations made by Kocher, Keverdin,
^** *" Fano, SchifT, Vassale, and others have shown them to be
important organs of metabolism, eliminating poisonous
matter from the system, and their removal by operations is
often followed by serious morbid symptoms.1 The pineal
gland, another organ formerly called rudimentary, and supposed
to be a remaining trace of a third eye possessed by our animal
ancestors, has now been recognised by Cyon as an organ
securing equilibrium, and regulating the circulation of the
blood at the base of the brain. It is quite possible that in
course of time other ' rudimentary organs ' will be found to
serve some definite purpose. In the case of some, e.g. the
atrophied muscles of the human ear, it is likely that they were
better developed at some early period in the history of the
human race, and degenerated later. This may be true also
of the famous vermiform appendix of the coecum, at least in as
far as a pathological formation is concerned, which often gives
rise to morbid symptoms.2
(b) The Biogenetic Law and its Application to Man
But I may be asked — is it true that man in his embryonic
development still passes through all those stages in rapid
succession, through which his ancestors have once passed
L~^4 in their phylogeny ? — for this is what should occur according
to the^ famous biogenetic law,, of which Meckel and Charles
^ ^ Darwin had some idea, although it was first enunciated by
£ -</!Fritz Miiller, and afterwards elaborated by Ernst Haeckel
^T (1866).
If we could trust Haeckel, we should have to answer this
•y question in the affirmative. The first and second stages, in
*J*^I - i gee o. Schulz, 'Neuere und neueste Schilddriisenforschung ' (Biolog.
Zentralblatt, XXXVI, 1906, No. 21, pp. 754-768).
2 See W. Ellenberger, ' Beitrage zur Frage des Vorkommens, der anato-
mischen Verhaltnisse und der physiologischen Bedeutung des Coecums, des
Processus vermiformis und des cytoblastischen Gewebes in der Darmschleim-
haut ' (Archiv /. Anatomie u. Physiologic, Physiolog Abtlg. 1906, pp.- 139-186).
HAECKEL'S ANTHROPOGENY 447
which the human ovum is unicellular, would be a repetition
of the Moneron and Amoeba stages in the phylogeny of man.
The third or Morula stage would be a repetition of the Syna-
moebae. The fourth or blastula stage would be that of the
Planaeada. The fifth or gastrula stage would be that of the
Gastraeada, for these imaginary creatures consisted simply
of a stomach. The sixth stage in the ontogeny of man would
repeat that of the primitive or low worms, the seventh that of
the soft worms, and the eighth that of the Chordata. This
completes the first half of man's pedigree according to
Haeckel. The second half begins with the Ascidia.
Next to the Chordata stage comes the ninth, in which the
human embryo resembles the Acrania, or skull-less animals,
which are represented now by the famous lancelet (Amphioxus
lanceolatus). The tenth stage is that of the single-nostriled
animals or Monorrhina, when we had round, sucking mouths.
The eleventh is that of the primaeval fish, when our ancestors
had fins and gills, and presented the pleasing appearance of
sharks. The twelfth stage is that of the mud-fish, the thir-
teenth that of the gilled Amphibians, and the fourteenth that
of the tailed Amphibians. The fifteenth stage in the embryonic
development of man is that of the primitive Amniotes ; the
sixteenth is that of the primitive mammals or Promammalia ;
the seventeenth is that of the pouched animals or Marsupials ;
the eighteenth is that of the semi-apes or Prosimiae; the
nineteenth is that of the apes with tails ; the twentieth is that
of the anthropoid apes ; the twenty-first is that of the ape-like
men or Pithecanthropi ; and finally, at the twenty-second stage,
we arrive at Homo sapiens, and as such the infant enters the
world at his birth.
There is no need to compose a satire upon Haeckel's
' Anthropogeny.' It made its appearance in 1874 and has
since passed through several editions. It is enough to
enumerate the twenty-two phylogenetic stages which the
human embryo is supposed to ' recapitulate ' before his birth,
and this theory at once reveals itself as a fiction devoid of
all foundation.
Some quite superficial resemblances between certain stages
in the development of the human embryo and the final forms
of other creatures, ranging from unicellular Amoebae to
448 MODEKN BIOLOGY
vertebrates, have been taken as the basis of a phylogenetic
analogy, that has been drawn with more daring than logical
accuracy. The gaps in the lineof man's ancestry have been filled
up with fanciful creatures, existing only In the imagination and
described as primitive gastraeada, primitive amniotes, primitive
promammals, primitive marsupials, pithecanthropi, &c., and
then we are told to regard this pedigree as a scientific proof
of the descent of man from beasts, in accordance with the
biogenetic law !
Haeckel's phylogenetic stages in human embryonic develop-
ment, as set forth in his ' Anthropogeny,' have already increased
in number from twenty-two to thirty.
They are given in his lecture on our present knowledge
of the origin of man, published in 1899 (' Uber unsere gegen-
wartige Kenntnis vom Ursprung des Menschen,' pp. 36, &c.) and
there they bear the highly scientific name ' Progonotaxis of
Man.' In Haeckel's latest work, ' Der Kampf um den Entwick-
lungsgedanken,' } which contains his three lectures delivered
in Berlin, we find the same Progonotaxis on pp. 96, 97.
It is the same sort of hoax — I know no milder expression
applicable to it2 — which Haeckel has been perpetrating for
over twenty years, but it appears in an enlarged and by no
means improved form. From the imaginary monera — those
non-nucleate organisms that have no existence — he leads
us along a series of thirty stages, each one decked out with
high-sounding, scientific phraseology, until finally we reach
the Homines loquaces — the speaking — or, more accurately, the
chattering men of the present day. It would be a waste of time
to dwell at greater length upon this fictitious series, by means
of which Haeckel strives to show that he has successfully
applied the biogenetic law to man.
Even if the ' law ' had good reason for its existence, such
an application of it to man would still be, to say the least,
1 ..The title of the English translation is Last Words on Evolution.
2 Some critics, e.g. K. Escherich, in the Supplement to the Attgemeine
Zeitung (see « A few Words to my Critics ' in the preface to this edition), have
found fault with me for having ' disparaged and ridiculed those scientific men
who established and developed the theory of evolution.' The reference is no
doubt to my use of words such as ' mischief,' * hoax,' &c., in speaking of
Haeckel. If Haeckel does not hesitate to make mischief and to perpetrate
hoaxes in the name of science, no reasonable man will take it amiss that I
feel bound to describe his methods in such language.
THE BIOGENETIC LAW 449
purely arbitrary. But we must now consider whether the
biogenetic law has really any justification.1
Do facts warrant the assertion that the individual develop-
ment of every creature is invariably an abridged recapitulation
of the history of the race ? No, they do not ; for the exceptions
to this rule are far more numerous than the instances of it.
The majority of the stages in the evolution of the individual,
through which the various species of animals pass at the
present day, do not correspond to the hypothetical stages in the
history of the race. Haeckel himself had an inkling of this
truth, but he very cleverly tried to avoid the difficulty by
distinguishing two elements in the ontogeny of the individual,
viz. palingenesis (Trahw-'yevecns), which is a recapitulation of the
stages corresponding to the evolution of the race, and cceno-
genesis (/caivr; yeveo-is), which is a collective name applied to
deviations from it. According to Haeckel, caenogenesis
is a falsified or disturbed development, tolerated by nature
under the compulsion of adapting the embryonic development
of various organisms to altered circumstances. Haeckel
was unhappy in his choice of words when he described the
evolution as falsified ; I should prefer to believe the falsification
not to be on the part of nature in dealing with her own laws, but
on the part of the prejudiced discoverer of these so-called laws.
It is impossible to maintain that the biogenetic law is a
general law, giving an account of the ontogeny of the individual
in accordance with the hypothetical phylogeny of the race.
Haeckel goes so far as to refer to this * law ' the processes
of segmentation, by means of which a multicellular organism
is produced from a fertilised egg-cell, and he sees in this process
a recapitulation of the phylogenetic development of multi-
cellular animals from primitive unicellular forms. There
is no justification at all for this theory, for, as Oskar Hertwig
remarks in his ' Allgemeine Biologie ' (p. 596) : ' The whole
nature of a unicellular organism makes it impossible for It
1 For criticisms of it see especially 0. Hertwig, Allgemeine Biologie, 1906,
chapter 28, pp. 592, &c. ; K. Fleischmann, Die Deszendenztheorie, 1901, chapters
13 and 14 ; J. Reinke, Studien zur vergleichenden Entwicklungsgeschichte
der Laminariaceen, Kiel, 1903, No. 13 ; Die Laminariaceen und Haeckels
biogenetisches Grundgesetz, pp. 57, &c. ; A. Oppel, Jahresberichte iiber die Fort-
schritte der Anatomie und Physiologie, XX, 1892, p. 683 ; Karl Vogt, Beard,
Hensen, Emery, Driesch, and others have also expressed their disbelief in
the truth of the biogenetic law.
2 o
450 MODEEN BIOLOGY
to be changed in any other way than by cell- division ; therefore
the ontogeny oT every living creature must inevitably begin
with a process of cleavage? This process has nothing whatever
to do with th(T hypothetical phylogeny, for if there were no
phylogeny at all, a multicellular organism could develop,
grow and propagate itself only by way of cell-division. Con-
sequently there must be some degree of resemblance between
the processes of individual development in different organisms,
as all alike are subject to the general laws of cell-division.
The same idea is expressed by 0. Hertwig (p. 595), when he says :
' That certain phenomena recur with great regularity and
uniformity in the development of different species of animals,
is due chiefly to the fact that under all circumstances they supply
the necessary conditions under which alone the next higher
stage in the ontogeny can be produced?"
These resemblances in the embryonic development of
animals of various species have therefore nothing whatever
to do with the hypothetical phylogeny.
Oskar Hertwig (p. 593) proposes to make some modifications
in, and to add some elucidations to, the biogenetic law as
understood by Haeckel. He says : ' We must leave out
the words " recapitulation of forms of extinct ancestors,"
and substitute for them, " repetition of forms regularly occur-
ring in organic development, and advancing from the simple
to the more complex." We must emphasise the fact that in
the embryo, as well as in the full-grown animal, the general
laws governing the development of living organic matter
are at work.' By this statement Oskar Hertwig has not
* modified ' the biogenetic law, but has simply overthrown it ;
for I cannot discover, in his manner of interpreting it, any
suggestion of a recapitulation of the hypothetical phylogeny,
but a repetition of general conformity to law in the develop-
ment of living creatures.
In his ' Morphogenetische Studien ' (Jena, 1903) Tad.
Garbowski uses very similar expressions. He says : ' Most
of what is generally ascribed to the action of the so-called
biogenetic law is erroneously ascribed to it, for all that is
undeveloped and incomplete must be more or less alike.'
As causal factors in the development of every individual,
we have to distinguish three things : —
THE BIOGENETIC LAW 451
1. The general laws of growth in living matter, which
depend upon the processes of cell-maturation and fertilisation,
cell-division and cell-growth.
2. The special lines followed by these processes in conse-
quence of descent from definite ancestors, or, in other words,
owing to the direct action of heredity.
3. The special lines followed by these processes of growth
in consequence of the adaptation of the organism to exterior
influences, these being subsequently fixed by heredity.
The biogenetic law owes its origin to the fact that the
second of these three factors has been violently torn from
its natural connexion with the other two, and has been raised
to the rank of an independent and universal * law.'
The biogenetic law is not a fundamental law, but only
under the most favourable circumstances is it even a partial
law. The method by which it has attained its position is
—when viewed from the standpoint of the theory of evolution —
absolutely one-sided, and therefore altogether wrong, and in
the twentieth century men of science should not be slow-
to perceive this.
E. Koken remarks very justly l that the biogenetic law
originated in a superficial view of facts. ' The biogenetic
law informs us that ontogeny in general is a recapitulation
of phylogeny. Phylogeny however tells us that it too does
not proceed at random, but is directed by the material on
which it works, just as ontogeny is influenced by the plasm
of the egg-cell.' Thus, just as in the fertilised ovum the
tendency to develop is the real Anlage or basis of the indi-
vidual development, so the tendency to develop, possessed
by the primitive forms of the race, is the real Anlage or basis
of the hypothetical development of the race. This is the true
parallel between ontogeny and phylogeny.
Let us now turn once more to human embryonic develop-
ment. We cannot be surprised if it bears a vague general
resemblance, in some of its stages, to what may be permanent
forms in the case of other animals. We should indeed expect
to find such a likeness, for, in conformity to its inner nature,
embryonic development, being dependent upon the processes
1 Paldontologie und Deszendenzlehre, 1902, p. 226.
2 o 2
452 MODERN BIOLOGY
of growth, must make use of them, and must advance from
what is simple to what is compound, and from what is general
to what is particular.
It must, therefore, begin with a unicellular stage and
pass through various multicellular stages, gradually approxi-
mating more and more closely to the final form at which
the development aims. The development of the embryo
as a whole, as well as of its single parts, must at different
stages display different degrees of perfection, until at last
the goal is attained. All these processes might occur succes-
sively in precisely the same way if no hypothetical phylogeny
had preceded them. How can we venture to affirm with
Haeckel that human ontogeny is quite unmistakably a recapi-
tulation of human phylogeny ? 1 Such a theory is a mere
matter of fancy !
There are, it is true, in the ontogeny of various animals
certain stages which can be accounted for causally only by
reference to the history of the race. This subject has been
discussed in the chapter on the theories of descent and evolution,
when, in speaking of the termitophile genus of Diptera known
as Termitoxenia, I alluded to the temporary formation of
real wing-veins in the development of the appendages on the
thorax, and said that their presence proved the ancestors of our
Termitoxenia to have been genuine Diptera.2
Similar phenomena occur in higher animals, although
very rarely. A century ago (1807), the very interesting dis-
covery was made by Geoffrey St. Hilaire, which has been
recently confirmed by Kukenthal," that the embryo of_a
whalebone-whale has teeth, although the adult whale has
whalebone plates instead of teeth. Palaeontological dis-
coveries show that the earlier fossil whales of the Tertiary
period were all toothed whales, retaining teeth throughout
1 This overhasty assertion was accepted as true by K. Escherich in his
criticism of the previous edition of my book (Beitrdge zur Allgemeinen Zeitung,
1905, No. 55). The remarks that I have made above may serve as an answer
to him as well as to Haeckel.
2 Cf. Chapter X, pp. 384, &c. ; also ' Die Thorakalanhange der Termito-
xeniidae, ihr Bau, ihr imaginale Entwicklung und phylogenetische Bedeutung '
(Verhandl. der Deutschen Zoolog. Gesellschaft, 1903, pp. 113-120 and Plates II
and III).
:i Cf. R. Keller, Das Leben des Meeres, Leipzig, 1893, p. 301, in the chapter
on aquatic mammalia.
THE BIOGENETIC LAW 453
their whole life. We are therefore not merely justified in
concluding, but we are almost forced to conclude, that our
present whalebone-whales are descended from toothed whales,
and that the foetal teeth are a phylogenetic reminiscence
which serves no biological purpose, as the whale embryo,
like that of all other mammals, has nothing to masticate.
Instances of this kind go far to prove that the theory of
descent is at least probably correct, for they admit of only
one interpretation. If it were possible to point to similar
stages in the ontogeny of man, admitting of only one inter-
pretation, viz. that they are after-effects of his earlier phylogeny,
we should have very weighty evidence in favour of the theory
that man, in respect of his body, is descended from brute
ancestors. But so far no such phenomena have been observed
in the case of man.
If we, for instance, examine closely the so-called * shark-fins '
and ' fish-gills ' of the human embryo, we shall find them
to be formations playing quite another part in the embryonic
life, ancT having therefore a direct reason for their existence
in the circumstances under which the embryo develops.
We are certainly not bound to infer from their superficial
likeness to real fins and real gills that our ancestors were
once fishes. In order to satisfy Escherich and other critics,
I should like to say a few words on the subject of the branchial
clefts and arches, which are regarded as traces of gills. They
occur in man and in all vertebrates, but only in fishes do they
develop into real, permanent gills. The embryo of man
and other mammals has on its neck four so-called branchial
clefts and three so-called branchial arches : ] the first branchial
arch is the largest, and eventually forms the oral cavity and
the parts belonging to it ; the second arch is less developed,
and the third is unimportant. Of the so-called branchial
clefts separating the arches, only one has any permanence
in man, it forms chiefly the external auditory meatus, the
others close up again. The three branchial arches partly
are transformed into particular organs, partly they become
cartilaginous and change into definite parts of the adult body,
either permanent or having some considerable duration.
1 See Ranke, Der Mensch, I, pp. 145, &c.
454 MODERN BIOLOGY
They form the Meckel's cartilage on the lower jaw, the two
delicate auditory ossicles, known as the malleus and incus,
as well as the hyoid bone and the styloid process. In fishes,
however, the embryonic branchial arches and clefts remain
and form the permanent gills. The pharyngeal arches and
clefts in the human embryo bear a superficial likeness to the
gills of fish, and so they have been called branchial arches
and clefts, whereas" they are really indifferent pharyngeal
extroversions in the embryo, supplying the material for other
subsequent formations. Can any one seriously regard them
as evidence that our forefathers were once fish, and that
the embryonic development ' recapitulates ' this former
fish-stage ?
Every thoughtful reader will see that there is a vast differ-
ence between fanciful interpretations of phenomena, such
as I have mentioned, and genuinely scientific attempts to
account for them.
Again, the young of the black Alpine salamander
(Salamandra atra) are born as land-animals, breathing by
means of lungs, but before their birth, whilst still in the
Fallopian tubes of the mother, they have large tufted gills
and a tail-fin like genuine water animals. In this respect
they exactly resemble the larvae of the spotted salamander
(S. maculosa), which are born at an earlier stage of development,
and are at first aquatic, so that they really use their gills and
tail-fin, before they become land-animals. The question
naturally occurs : ' Why have the larvae of the Alpine sala-
mander gills and tail-fin, when they never, at any period of
their life, can use them ? ' The only obvious answer is :
' Because, like the larvae of all other Urodela, they were
originally intended to live in water, and subsequently, in
consequence of the period of development being shortened,
they wrere born as complete land animals.'
The difference is obvious between the real gills of these
salamander larvae and the imaginary gills, which the human
embryo is said to possess as a reminder of the time when
his ancestors were fish.
Again, if we consider the ontogeny of certain parasitic
Copepods among the Crustaceans, e.g. in the genus Lernaea
(see Chapter X, p. 327, note 1), we shall find that at an early
THEOBIES ON THE DESCENT OF MAN 455
stage these creatures resemble other Copepod larvae, but the
adult female's body is simply a bag of eggs, and is shaped like a
sausage. It cannot be denied that in this case the ontogeny
of the individual suggests unmistakably that the parasitic
genus Lernaea is descended from Copepods once leading an
independent existence, and gradually adapted to a parasitic
way of life. But I say again emphatically : in the ontogeny
of man we know of no such phylogenetically unquestionable
phenomena.
The resemblances between the human embryo and that
of the other vertebrates are so superficial that His, W. von
Bischof, and even Karl Vogt, and many other recent and
thorough students of comparative embryology, have protested
against Haeckel's regarding these resemblances as phylogene-
tically significant identities.1 Nothing but gross want of
knowledge can excuse a man at the present day for bringing
forward this argumentum ex ignorantia in support of this
descent of man from beasts.2
We might perhaps close our investigation of the zoological
evidence for the descent of man from beasts at this point.
It may, however, be well to give a short sketch of the two chief
theories on this subject, so that the reader may know how the
question stands at the present day.
These two theories are antagonistic to one another. The
first is practically only an extension of Karl Vogt's Ape-
theory. It assumes a direct relationship between man and
the anthropoid apes, the so-called primates, and, with Frieden-
thal, it proclaims man to be simglya genuine ape. The second ' »
theory on the contrary denies that man is directly related to
the present apes, but admits the existence of a distant, indirect
connexion, inasmuch as it traces the descent of both from a
hypothetical common stock, which is supposed to have lived in
the Older Tertiary or Pre- Tertiary period.
1 The story of the three illustrations by means of which Haeckel tried
to prove this identity in his History of Creation, is too well known for it
to be necessary to discuss it here. Cf. 0. Hamann, Entwicklungslehre und
Darwinismus (1892), pp. 26, &c. Also E. Dennert, Die Wahrheit uber Ernst
Haeckel und seine Weltrdtsel, 1904, chapter iii, p. 16, &c.
2 On this subject see J. Ranke, Der Mensch, I, pp. 152-154.
456 MODEKN BIOLOGY
(c) The Theory that Man is directly related to the Higher Apes
Let us now examine more closely the first of these two
theories. It is held by many modern zoologists, and the
following evidence has recently been adduced in support of it.
Selenka discovered that the higher apes resemble man during
their embryonic development in having a simple discoid
placenta, whilst the lower apes have a bidiscoidal placenta.
It would, however, be rash to regard this discovery as a proof
of direct relationship between man and the higher apes, the
value of the new piece of evidence is not greater than that
afforded by a number of other well-known morphological
and embryological resemblances between man and apes, for
in this case also the question arises : ' Are these resemblances
the result of close relationship, or are Jhey merely converging
phenomena, due, not to community of origin, but to adaptation
to similar conditions of life or development ? '
The following consideration shows how much caution is
necessary in regarding the formation of the placenta as evi-
dence for the theory of descent. In the Monotremes, which
are the lowest mammals, the placenta is absent, and in the
Marsupials it occurs only rarely and in a very imperfect
form, but the higher mammals are called placentals, as the
possession of this organ distinguishes them from the two
former subclasses. On the other hand, as Aristotle discovered,
and as Johannes Miiller found in the nineteenth century, a
placenta occurs in the smooth shark (Mustelus laevis) and in
its relations belonging to the genera Mustelus and Carcharias,
only its vessels are supplied by the yelk-sac, and hot, as in
mammals, by the allantois. Quite recent research is believed
to have revealed the presence of a placenta even in some
Arthropods, Kennel has seen it in the American Peripatus,
and Poljansky in the Indian scorpion.1 This shows that the
existence of a placenta, and still more its peculiar structure,
havenoi.jiecessarily , anything to do with a direct^elationship
Otherwise we should be
obligeooregard the Indian scorpion as the ancestor of the
placental mammals, the highest of which is man.
1 Zoolog. Anzeiger, 1903, No. 2, pp. 49-58.
FBIEDENTHAL'S EXPEKIMENTS 457
No zoologist would venture to draw such a conclusion, but
he would prefer to ascribe the occurrence of a placenta in such
diverse kinds of animals to independent convergence, as the
formations are merely analogous and not homologous.
Not long ago, Dr. Hans Friedenthal1 thought that he had
discovered fresh evidence proving man to be directly related to
the primates. As his communications have attracted a good
deal of attention in circles interested in popular science, and
will probably continue to do so, I propose to examine them
critically.
Friedenthal has made a number of experiments, that are
neither complete nor conclusive, with a view to investigating
the transfusion and reaction of blood. The blood-relationship,
that he professes to have discovered between man and the
primates, is based upon his observation that human blood
destroys the red corpuscles in the blood of the lower apes, but
has no such effect upon that of the anthropoid apes. Whether
this is a fact or not is still very doubtful, for not many experi-
ments have been made, and the results of those that were made
are not altogether uniform. In some cases the serum of the
blood of a lower ape (Macacus sinicus) destroyed the red
blood discs in human blood, and in other cases it did not. We
do not yet know whether the serum of human blood never
destroys the red blood corpuscles in the blood of the anthropoid
apes, and vice versa. Friedenthal acted somewhat prematurely
in using some probabilities as the foundation of a general law,
according to which he proclaimed man to be a blood-relation
of the higher apes.
Antiserum and blood-serum have opposite results in
experiments on reaction. Antiserum is derived from animals
which have been rendered immune from the destructive action
of the blood-serum of another species ; and it affects only
harmonic or similar kinds of blood, and has no effect upon
dissimilar. Nuttall 2 has examined the blood of eighteen kinds
1 ' tiber einen experimentellen Nachweis der Blutverwandtschaft '
(Archiv fur Anatomie und Physiologic, Physiolog. Abt., 1900, pp. 494-508);
' Neue Versuche zur Frage nach der Stellung des Menschen im zoologischen
System ' (Sitzungsberichte der Kgl. Akademie der Wissensch. XXXV, Berlin,
July 10, 1902, pp. 830-835.
2 G. H. F. Nuttall, ' The new biological test for blood in relation to zoological
classification ' (Proceed. Royal Society, London, LXIX, 1901-1902, No. 453,
pp. 150-153) ; Blood Immunity and Relationship, London, 1904. Cf. also
458 MODEBN BIOLOGY
of apes in its relation to human blood, and has found that
they all showed reaction to the antiserum of human blood,
but in very different degrees. Anti-ox-serum showed reaction
also, not only to the blood of other Bovidae, but also, though
in a less marked degree, to the blood of sheep, goats, antelopes,
and gnus, although these animals are systematically not
closely related to the Bovidae.
Even if it is definitely proved that human blood possesses
certain chemico-physiological properties in common with the
blood of the anthropoid apes, whilst these properties are
wanting to that of the lower apes and other vertebrates, we
shall still not be able to infer from this proof that there is a
direct blood-relationship between man and the primates in
the sense of the theory of descent. Such an inference would be
based upon an obvious confusion of twojjuite different ideas,
viz. resemblance in the chemical properties of two ldnds~of
blood, and identity of phylogenetic origin of two kinds of blood.
If anyone confuses these two ideas by skilful jugglery, the
blood-relationship between man and the chimpanzee may
indeed appear to be proved — but only to an uncritical public.
The proof will be logically convincing only if it has been pre-
viously established, that a similarity in the chemical reaction
of two kinds of blood depends solely upon the existence of
direct blood-relationship between the animals possessing this
blood, and no one can maintain this to have been established.
Friedenthal Himself declared not long ago that the haemolysis
of the serum of any species depended also upon other factors,
quite unconnected with genealogical relationship. In the case
of the serum of eel's blood the reaction upon the blood of other
vertebrates is greatest, with the serum of the blood of amphibia
it is weak, with that of reptiles and birds it is strong. From
the chemical reaction of two kinds of blood upon one another
it is impossible to draw any inference for or against the relation-
ship of the animals in question. According to Friedenthal's
own experiments, the blood of a Crustacean (the common crab,
Cancer pagurus) or that of a lug-worm (Arenicola piscatorum)
did not destroy the red blood corpuscles of a sea-mew or a rat ;
E. Abderhalden, ' Der Artenbegriff und die Artenkonstanz auf biologisch-
chemischer Grundlage ' (N aturwissensck. Rundschau, XIX, 1904, No. 44,
pp. 557-560).
FKIEDENTHAL'S EXPEEIMENTS 459
but surely no one would infer that, for this reason, rats must be
directly descended from lug-worms, or seamews from crabs !
Nor is there any justification for drawing such an inference
when we meet with the same phenomenon in connexion with
the blood of man and of the orang-utang. We might in fact
reverse the whole argument and say : * Just as the rat cannot
be the direct descendant of the crab, nor the sea-mew of the
lug-worm, so man cannot be directly descended from an orang-
utang, for his blood reacted upon that of an orang-utang no
more than the blood of a crab upon that of a rat, or the blood
of a lug-worm upon that of a sea-mew.'
Arguments, that need only to be simply reversed in order
to prove the exact opposite of what they are intended to show,
are obviously very weak. One and the same phenomenon, viz.
the chemico-physiological indifference of two kinds of blood
towards one another is interpreted in two different ways in
Friedenthal's account of his experiments, according as it suits
his purpose. On the one hand, mutual indifference of the
blood of man and the anthropoid apes is due to the great
similarity between them ; on the other hand, mutual in-
difference of the^blood of the lower animals and vertebrates
is due to the great dissimilarity between them ; the same
result is referred to two totally opposed causes according to
Friedenthal's subjective requirements !
The experiments made in the last few years by Bordet,
Wassermann, Schiitze, Stern, Friedenthal, Nuttall, Uhlenhut,
and others with the serum and antiserum of the blood of a
great variety of animals are no doubt of great scientific interest,
and in many cases they supply us with valuable clues towards
establishing the systematic relationship of various kinds of
animals. Men of science will gradually learn to avoid Frieden-
thal's mistake of overestimating the importance and bearing
of the information thus supplied. All that we can learn from
such studies with regard to man is that he stands nearer to
the higher than to the lower apes and other mammals in the
composition of his blood, just as he has long been known to
stand nearer to them in respect of the tissues and organs of his
body. This line of research will not reveal more. As soon
as an attempt is made to ascertain the phylogenetic relationship
of animals from the reaction of antitoxins, the defects in this
460 MODEEN BIOLOGY
method become apparent, as well as its advantages. They
have both been discussed recently by Eobert Rossle.1 These
reactions do no more than furnish ' a standard of slight absolute
value for estimating the degree of relationship ; the reaction
justifies this comparison : ' animal A is more closely related
to animal B than is animal C ' ; but it gives us, strictly speak-
ing, no means of judging how close the relationship is.' It
would therefore be a serious mistake to conclude with Frie-
denthal from the reactions of the blood of men and apes that
man is descended from the higher apes, or that he is merely a
higher ape himself. Rossle considers that there is no reason
for assuming that the chemical composition of the fluids in
the body is more constant than the formation, for instance,
of the skeleton. If he is right, the chemico -physiological
resemblance between the blood of man and that of the primates
is less important, from the standpoint of evolution, than the
resemblances in the structure of their skeletons. Moreover,
we have learnt from the experiments in reaction made during
the last few years, that many actual contradictions are involved
in the theory that the chemico-physiological resemblance of
two kinds of blood, which is known as ' blood-relationship,' really
involves identity of origin. Rossle remarks on this subject :
' Again, an antiserum shows us two animals as closely connected,
whilst they are far apart in the morphological system.'
Finally — and this point is particularly important in our
present discussion, — recent investigations have shown the
physiological identity of the blood of man and of primates
(which Friedenthal maintains) to be at least very doubtful. At
the Anthropological Congress at Greifswald in 1904, Uhlenhut
spoke of positive reaction, that he had observed, of human
antiserum with the blood of lower apes. Friedenthal himself
lately mentioned having obtained positive results by mixing
human antiserum with the blood of Lemuridae. These
statements destroy the force of any evidence based upon such
reactions and adduced in support of the direct relationship
between man and the anthropoid apes. It seems as if the
wish had been the father of the thought in investigating their
1 ' Die Bedeutung der Immunitatsreaktionen fur die Ermittlung der
systematischen Verwandtschaft der Tiere ' (Biolog. Zentralblatt, 1905, Nos.
11 and 12).
FKIEDENTHAL'S EXPERIMENTS 461
alleged blood-relationship, and more unprejudiced research
may altogether remove the enthusiasm with which this dis-
covery was greeted. The latest ultra-microscopical examina-
tions have revealed in human blood certain peculiarities, which
were hitherto quite unknown. Eaehlmann l Ms examined the
blood of man and of various animals, and has discovered very
considerable differences in the ultra-microscopical structure
of the red-blood corpuscles. In human blood, for instance,
within the strongly marked diffraction rings at the outside
of the blood corpuscles, there are one or two polar bodies
which do not occur in the blood of other animals, but are
replaced by quite different formations. Finally, Brumpt has
succeeded in establishing the fact that sleeping-sickness, which
is conveyed by parasites in the blood (trypanosomes), can be
produced in all mammals by inoculating them with the blood
of a person suffering from the disease, the only exceptions
being a few apes and the pig (La Nature, April, 28, 1906,
Nos. 17 and 18, p. 339). As this inoculation involves a reaction,
just as much as the experiments on blood-relationship, we
should have to infer from these results that human blood
is * less closely related ' to that of apes and pigs than to that
of other mammals. In future more prudence ought to be dis-
played in drawing inferences of this kind !
It is therefore obvious that the newest ' proofs ' of the
blood-relationship between man and the primates do not justify
the conclusion that has been based upon them, and Hans
Friedenthal's triumphant statement, made on the ground of
the alleged blood-relationship between man and the higher
apes — ' We are not merely the descendants of apes, but
we are ourselves genuine apes ' — is seen to be devoid of all
justification.
Hitherto absolutely no real proof has been adduced of the
ape-theory, i.e. the theory that man is directly related to the
higher apes. I may venture to say that in all probability no
proof ever will be adduced, for this theory is quite irreconcil-
able with the second of the above-mentioned theories regarding
the descent of man from beasts, and there is far more evidence
in support of the latter.
1 Cf. W. Berg, ' Ultramikroskopie ' (Naturwissensch. Rundschau, 1906,
No. 28, pp. 353, &c.).
462 MODEEN BIOLOGY
(d) The Theory of the Remote or Indirect Relationship between
Man and Apes
Let us now turn to this second theory, according to which
man is not direclly descended from the primates, and is in fact
not closely related to them. This theory regards man on the
one hand, and apes on the other, as the extremities of two
lines of evolution, absolutely independent of one another, but
meeting in a purely hypothetical common ancestral form,
which existed at the beginning of the Tertiary period, or
probably even earlier. This opinion is held by Professor
Klaatsch ] of Heidelberg, M. Alsberg,3 C. H. Stratz,3 and many
other anthropologists.
What are we to think of this theory ?
In itself it is far more acceptable than the ape-theory. It
takes into account the phenomenon upon which much stress
has been laid by the most eminent anthropologists, Johannes
Kanke, Eudolf Virchow, Julius Kollmann, and others, viz.
that the bodily structure of man and apes respectively repre-
sents two distinct lines of evolution among mammals, diverging
widely at their extremities. In some respects, for instance
in the development of the hands, the apes have outstripped
man, and left him at a comparatively backward stage. Con-
sidered from the point of view of the evolution theory, the
human hand bears far more resemblance to that of the_zo.o-
logically lower apes than to that "of the highest anthropoid
apes, and the human foot is rendered quiteunlike the prehensile
foot o^ an apeTry the peculiar position of the big toe. I do
not, however, propose to discuss the bodily differences"between
man and ape in this place. They are stated very fully in J.
Eanke's ' Der Mensch,' and Bumiiller's little work, * Mensch
oder Affe ? ' (Man or Ape ?),4 contains a very clear description
of them.
The more perfect development of the brain and the upright
1 ' Entstehung und Ent.wicklung des Menschengeschlechts ' ( Weltall und
Menschheit, edited by Hans Kraemer, II, 1903, pp. 1-338).
2 Die Abstammung des Menschen und die Bedingungen seiner Entwicklung,
Cassel, 1902.
3 NaturgescJiichte des Menschen, Stuttgart, 1904 ; Zur Abstammung des
Menschen, 1906.
4 Ravensburg, 1900. Cf. my remarks on p. 438 and p. 446, note 1.
KLAATSCH'S THEOKY 463
position that it necessitates, which is connected with further
corresponding differences in the structure of the extremities —
these are the chief points bearing upon our subject, and, when
they are considered in their purely zoological aspect, they justify
our regarding man, in respect of his body, as forming a special
order among mammals. On this point, but only on this, I
agree with Moritz Alsberg,1 who sums up the results of investi-
gations made by Klaatsch and other anthropologists in the
following terms : ' That man is directly descended from
apes is inconceivable, and it is possible to speak of relationship
existing between man and ape only in as far as both are ulti-
mately connected at the root of their common genealogical
tree, and this applies to all mammals.'
Are we then to adopt this view of the descent of man from
beasts ? I am far from doing so, for the following weighty
considerations are opposed to it.
Firstly. Klaatsch assumes the existence, in the Tertiary
or Pre-Tertiary period, of a hypothetical common ancestor of
men and apes ; but such an ancestor exists only in his
imagination.2 The properties ascribed to this original form,
that he calls the ' general pithecoid type,' are so vague and
indefinite, and to some extent so conflicting, that I cannot
help regarding this primitive ancestor of man and ape as a
Universale a parte -rei, incapable of any real existence.
At the Anthropological Congress at Lindau in 1899, in
speaking of Klaatsch's opinions, Johannes Kanke remarked :
' Whilst a charming picture of the past and possibly of the
future is being shown us, and whilst a fanciful design is being
carried out in all directions, we are as a rule in quest of facts,
not of theories. The facts, however, upon which Herr Klaatsch
claims to base his ingenious theory, do not at present exist,
and I must protest against his assuming that they have been
really furnished by zoology and palaeontology any more than
by anatomy. . . . All else is still a matter of hypothesis, and
if anyone attempts to use it in order to produce a finished
picture, the result is a work merely of the imagination.'
Secondly. In considering the origin of man, we must
1 Die, Abstammung des Menschen und die Bedingungen seiner Entwicklung,
pp. 77-78.
2 Cf. also Stimmen aus Maria-Laach, LVIII, 1900, pp. 471-477.
404 MODEKN BIOLOGY
have recourse to palaeontology as well as to comparative
morphology. We must inquire what the former science can
tell us of the ancestors of man from their fossil remains, and
the further back we set the existence of the hypothetical
common ancestor of man and apes, the more forms shall we
call upon paleontology to show us intermediate between
this common ancestor and the modern representatives of
the two lines descended from him.
What answer does paleontology make to our question?
She does not merely say : ' The missing link between man
and ape has not yet been discovered.' Klaatsch's theory does
not indeed admit of the existence of a direct link between
the two. But palaeontology tells us far more than this, and,
relying on the results of most recent investigations, she says :
* We have the pedigree of the present apes, a pedigree very
rich in species and coming down from the hypothetical ances-
tral form of the oldest Tertiary period to the present day.
Zittel's " Grundziige der Palaontologie " gives a list of no
fewer than thirty genera of fossil Pro-simiae and eighteen
genera of fossil apes, the remains of which are buried in the
Various strata from the Lower Eocene to the close of the Alluvial
epoch, but not one connecting link has been found between
their hypothetical ancestral form and man of the present
time : the whole hypothetical pedigree of man is not supported
by a single fossil genus or a single fossil species.'
How extraordinary ! If man were really descended from
a prehistoric ancestor, common to him and to the apes of the
present day, there must surely be some fossil trace left of his
branch of the genealogical tree, and not only traces of the
branch leading to apes ! l
I should like to commend this scientific truth to the serious
consideration of all those who regard the descent of man from
1 It might, perhaps, be possible to raise the objection that the evolution
of the prosimiae and of the true apes was a slow and gradual process, and
that of the human race rapid and sudden. This might account for the absence
of fossil forms standing between the hypothetical primary form and modern
man. But this statement cannot be reconciled with the palseontogical
fact that man did not appear upon the earth before the Alluvial epoch. If
he had been evolved rapidly and without any long transitional stages from
an early Tertiary form, we should certainly find traces of Tertiary man as
well as of Tertiary apes. Cf. on this subject R. de Sinety, ' L'Haeckelianisme
et les idees du P. Wasmann sur 1'evolution ' (Revue des Questions Scientifiques,
January 1906), reprinted separately, p. 18.
PITHECANTHEOPUS ERECTUS 465
beasts as actually proved, or who hope that it will be actually
proved in the near future. As a critical student of nature, I
am bound to express my fears that the upholders of this theory
will find themselves disappointed.
3. CRITICISM -OF KECENT PAL^ONTOLOGICAL AND PRE-
HISTORIC EVIDENCE FOR THE DESCENT OF MAN FROM
BEASTS.
(a) The Upright Ape-man (Pithecanthropus erectus)
Let us now turn to the consideration of certain points
which have recently been brought forward by students of
palaeontology and early history as evidence of the descent of
man from beasts.
We must consider first the famous ape-man, Pithecan-
thropus erectus, of Java. So far the only remains that we
have of him are a cranium, a femur or thigh bone, and two
molar teeth discovered in 1891 in Pliocene deposits near
Trinil by Eug&ne Dubois, a Dutch military surgeon, who gave
an account of them in an address delivered at the Third Inter-
national Congress of Zoologists in Leyden, in September 1895.
He sought to prove that the creature, which he reconstructed
from these remains, was neither man nor ape, and could only
be a connecting link between them. Virchow, as president of
the meeting, uttered a very courteous but crushing criticism
upon the speaker's remarks, and showed that it was by no
means certain that the remains had all formed part of the
same individual, and that it was still less possible to decide
whether that individual was a man or an ape, since the femur
resembled that of a man, but the cranium seemed to be more
like that of an ape. He went on to say that probably it would
not be possible to decide finally upon the systematic place of
the Pithecanthropus until a complete skeleton was discovered.
In spite of all the controversy concerning the ape-man in the
years following Dubois' discovery, Virchow's criticism still
holds good. It is nothing short of an outrage upon truth to
represent scanty remains, the origin of which is so uncertain
as that of the Pithecanthropus, as absolute proof of the descent
of man from beasts, in order thus to deceive the general public.
2 H
466 MODEBN BIOLOGY
It cannot be maintained that the Pithecanthropus erectus is
a real transitional form connecting man with the higher apes ;
for, as man and ape, from the point of view of comparative
morphology, are the extremes of two widely diverging lines
of evolution, there can have been no recent link between them,
living as late as the Pleistocene or late Tertiary period. More-
over, although the Pithecanthropus possesses many peculiarities
which seem to place him midway between ape and man, he
has also others of a quite different kind, which seem to assign
him a place between the lower and the anthropoid apes of the
present day.1
Professor Schwalbe would certainly do his utmost to assign
a high degree of importance to the Pithecanthropus, and to
place him as near as possible to man, yet he pointed out these
latter peculiarities in the course of his examination of the
famous calvaria from Java.2
For this reason Klaatsch, Schwalbe, Alsberg arid other
not over-sanguine anthropologists do not agree with Eugene
Dubois in regarding his Pithecanthropus as the long-sought
ape-man, who was described prophetically by Haeckel a
quarter of a century earlier. They prefer to regard him as a
lateral branch of the pithecoid stock, which, -in consequence
of so-called ' convergent phenomena,' approximates to man
in many respects. Therefore, the Pithecanthropus does not
belong to the pedigree of modern man, but to that of the
modern apes, and so he ceases to be a witness for the descent
of man from beasts. I may refer to a few recent opinions on
the subject of the Pithecanthropus, given by men who cannot
be suspected of partiality.
In his * Lehrbuch der Zoologie ' (seventh edition), Kichard
Hertwig alludes to the remains of the Pithecanthropus and
says : * The fragments were regarded by some as belonging
to a connecting link between apes and man, Pithecanthropus
erectus Dubois ; by others they were thought to be the remains
of genuine apes, and by others again to be those of genuine
men. The opinion that is most probably correct is that
the fragments belonged to an anthropomorphic ape of
1 Cf. also Alsberg, Die Abstammung des Menschen, pp. 100, &c.
2 In his Vorgeschichte des Menschen, 1904, p. 29, he again says that the
Pithecanthropus has no place in the genealogical line of man's direct ancestors.
THE NEANDEETAL MAN 467
extraordinary size and an enormous cranial capacity, and with
a relatively very large brain corresponding to this cranial
capacity (circa 850 c.cm.). The structure of the femur suggests
that the animal probably walked upright.' l
Macnamara has recently submitted the skull of a chimpanzee
and the much-discussed Pithecanthropus cranium to a very
careful comparison and examination, in consequence of which
he has arrived at a similar conclusion, namely that the Pithecan-
thropus was a true ape of large size.3 He examined both crania
according to Schwalbe's newest methods of taking measure-
ments. In fig. 53 (p. 469) curve IV represents the contour
of the Java cranium and curve V that of the chimpanzee
cranium. Almost the sole difference between them is in size,
and for this reason Macnamara gives it as his opinion that
* the cranium of an averge adult male chimpanzee and the
Java cranium are so closely related that I believe them to
belong to the same family of animals — i.e. to the true apes.' 3
(b) The Neandertal Man and his Contemporaries
The Pithecanthropus, however, no longer stands alone,
he has found a companion, rather younger than himself, in the
Neandertal man, who likewise is supposed to have been neither
a man nor an ape, such as now exist, but something between
the two. We owe this discovery to Professor Schwalbe of
Strassburg.4' The remains of the skeleton of the Neandertal
man were found in a cave near Diisseldorf in August 1856.
The cranium was described by Schaafhausen in Muller's
1 Whether this is the case or not might probably be determined by Walk-
hoff's method of X-ray photography. It has been suggested that the Pithec-
anthropus possessed the power of speech, because in his cast of the interior
of the Java calvaria, Dubois found the third inferior gyrus (Broca's convolu-
tion) to be double the size that it is in anthropoid apes, though only half
what it is in man (Schwalbe, Vorgeschichte des Menschen, p. 18). This
discovery on a skull that has been decaying for thousands of years is of a
nature no less problematical than is its psychological significance.
2 Kraniologischer Beweis fur die Stellung des Menschen in der Natur
(Archiv fiir Anthropologie, XXVIII, 1903, pp. 349-360).
3 If Macnamara nevertheless asserts that the Java cranium bridges the
wide interval between the anthropoid apes and the Neandertal man, his
assertion is unjustifiable, for the larger cranial capacity is not enough by itself
to justify it.
4 See G. A. Schwalbe, ' Der Neandertalschadel ' (Banner Jahrbiicher, 1901,
No. 106, pp. 1-72, with Plate I) ; also Stimmen aus Maria-Laach, LXI, 1901,
pp. 107, 108.
2 H 2
468 MODERN BIOLOGY
Archiv for 1858 in an article headed ' Zur Kenntnis der
altesten Rassenschadel.' Fig. 52 is a reproduction, reduced
in size, of Schaafhausen's photograph, giving a side view of
this famous cranium (1888).
Numerous articles have been written on the subject, arid
in 1901 another thorough examination of the skull was made
by Schwalbe, who finally pronounced the Neandertal man to
have been a representative of a distinct genus, standing
between ape and man. |
We must admire Schwalbe's ingenuity in adding a twelfth
FIG. 52. — Neandertal cranium.
to the already existing eleven opinions regarding the Neandertal
man, but he cannot claim any greater authority for his view
than the other writers can claim for theirs, which are quite
different. It has fallen to the lot of this Neandertal man to be
described variously as an idiot, a Mongolian Cossack, an early
German, an early Dutchman, an early Frieslander, a connexion
of the Australian blacks, a palaeolithic man, and a still more
primitive ape-man. The remains of his skeleton clearly are of
a nature to admit of many interpretations, and each student
can make of them whatever he wishes. It would be wrong to
assume that a discovery of this kind justifies scientific men
in declaring that they have found the long-sought missing
link between ape and man.
MACNAMAEA'S CURVES
469
FIG. 53. — Outlines of the sagittal median curves, drawn with
Lissauer's diograph :
I. Skull of modern Englishman.
II. Skull of modern Australian black.
III. Neandertal skull.
IV. Pithecanthropus skull.
V. Chimpanzee skull.
(After Macnamara.)
FIG. 54. — Outline of the sagittal median curve :
I. Of the skull of an early brachycephalic Lapp.
II. Of the skull of a dolichocephalic Australian.
III. Of the Neandertal skull.
(After Macnamara.)
470 MODEKN BIOLOGY
The uncertainty regarding the Neandertal remains is
increased by the fact that we have no means of judging their
geological age ; for, as Rauff l pointed out recently, no com-
petent judge saw the Neandertal skeleton, in its original
position (in situ). When Fiihlrott, its scientific discoverer,
reached the place where it had been found, the workmen in
the quarry had already thrown the loam containing the bones
out of the cave, and had partially destroyed the wall of rock.
For this reason K. Virchow remarked : ' Whether they (the
bones) were really in Alluvial loam, as is generally assumed, or
not, no one saw. . . . The whole importance of the Neandertal
skull consists in the honour, ascribed to it from the very
beginning, of having rested in Alluvial loam, which was formed
at the time of the early mammals.' 3
The famous Neandertal man may therefore have lived
after the loam was deposited in the cave, and his bones may
have become embedded in it later. If this were the case, all
speculations as to his importance to the theory of evolution
would simply fall to the ground. Virchow said of him : 3 ' We
may certainly regard it as decided that the brain-cast bears
no resemblance to that of an ape, and even if the cranium is
admitted to be a typical race-cranium (which I consider quite
unjustifiable), it does not by any means follow that we may
deduce from this that it approximates to that of an ape.'
Schaafhausen himself in 1888 * was content to say : ' In
making this discovery we have not found the missing link
between man and brute.' Recent investigations on the
1 ' tiber die Altersbestimmung des Neandertalmenschen und die geolo-
gischen Grundlagen dafiir' (Verhandl. des Naturhist. Vereins, Bonn, 1903,
pp. 11-90 with one plate). Cf. also on the same subject, H. Schaafhausen,
Der Neandertaler Fund, Bonn, 1888, pp. 7, &c. Fig. 52 on p. 468 of this book
is borrowed from Plate I of Schaafhausen's work. I ought to add that recently
a second human skeleton has been found in the Neandertal, but the skull
is missing. The fragments are designated Homo neanderihalensis II, and
are of late Alluvial origin, whereas Homo neanderthalensis I is believed to have
lived in the early Alluvial epoch, and to have been the real Homo primigenius.
Cf . Koenen, ' Zur Altersbestimmung der Neandertaler Menschenknochenfunde '
(Sitzungsber. der Niederrheinischen Gesellsch. fur Natur- und Heilkunde, Bonn,
June 10, 1901); ' Uber Eigenart und Zeitfolge des Knochengeriistes der
Urmenschen ' (ibid. February 9, 1903) ; ' Die Zeitstellung der beiden Neander-
talmenschen ' (ibid. June 8, 1903).
2 Quoted from Kanke, Der Mensch, II, p. 485.
3 Ibid. II, p. 478. On Virchow's attitude towards the doctrine of descent
and especially towards its application to man, see R. Otto, N aturalistische
und religiose Weltansicht, Tubingen, 1904, pp. 83-87.
4 Der Neandertaler Fund, p. 49.
MACNAMAEA'S CUKVES 471
subject of the Neandertal man and his Alluvial contem-
poraries all tend to confirm this statement.
In a paper read on September 23, 1903, at the 75th meeting
of German Naturalists and Physicians at Cassel, Dr. Schwalbe
discussed the early history of man,1 and attempted to show
that the Neandertal men ought to be considered a distinct
species, connecting the Miocene apes with man of the present
time ; he no longer ventured to speak of them as belonging
to a distinct genus, as he had done in 1901.
Science, however, refuses to accept this new human species,
which Schwalbe calls Homo primigenius, or primitive man,
and prefers to see in it merely an ordinary subspecies or breed,
such as still occurs in Australia.
N. C. Macnamara, an enthusiastic advocate of Schwalbe's
method of examining skulls, has shown still more recently,
in the Archiv fur Anthropologie,2 that crania, resembling
that of Homo primigenius in its various characteristics, occur
at the present day among the blacks in Australia and
Tasmania. In proof of this I may refer the reader to figs.
53 and 54 (p. 469), which are borrowed from Macnamara's
work. We see on fig. 53 that the cranium of a modern
Australian black (curve II) differs very slightly from that
of the Neandertal man (curve III), although both differ
greatly from that of a modern Englishman (curve I). In
fig. 54 curve I represents the cranium of an old brachy-
cephalic Lapp, curve II that of a dolichocephalic Australian
black, and curve III the Neandertal cranium, which is also
dolichocephalic. Here again we can easily see that the crania
of the Australian black and of the Neandertal man resemble
one another far more closely than they resemble the Lapp
cranium. Yet no one doubts that Lapps and Australian
blacks must both be included in the same systematic species,
known as Homo sapiens. In comparing the Australian and
the Neandertal crania with respect to these curves, Mac-
namara himself says (p. 358) : ' The average cranial capacity
of these selected thirty-six skulls (of Australian and Tasmanian
1 Die Vorgeschichte des Menschen. This paper was printed with additions
at Brunswick, 1904.
2 ' Kraniologischer Beweis fur die Stellung des Menschen in der Natur '
(Archiv fur Anthropologie, XXVIII, 1903, pp. 349-360).
472 MODEKN BIOLOGY
blacks) is even less than that of the Neandertal group, but in
shape some of these two groups of crania are closely related,1
as is apparent from the drawing of one of these skulls ' (fig. 54). 2
We may therefore safely conclude that the Neandertal cranium
lies within the limits of variation of the species Homo sapiens ;
Homo primigenius represents not a distinct species of man. but
only an early race of man.
In the course of the last few years Professor Gorjanovid-
Kramberger3 has very carefully compared Homo primigenius
of the early Alluvial epoch with Homo sapiens, having at his
disposal for the purpose the largest collection hitherto available
of fossil human remains. He believes Homo primigenius
(cf. fig. 52, p. 468) to differ from modern man chiefly in the
formation of the cranium (see Plate VII, A), with its low,
receding forehead and strongly marked supraorbital ridges,
in the bent occipital bone and in the large, prognathous
lower jaw, devoid of chin. But in all these respects Homo
primigenius displays numerous transitional forms gradually
approximating to modern man.
I may quote Kramberger himself on the subject : 4 ' This
short resume and my previous statements make it perfectly
plain that the Alluvial human remains hitherto discovered in the
Neandertal, at Spy, La Naulette, Schipka, Ochos, and Krapina,
all belong to one and the same species, namely to Homo primi-
genius. What I have said, however, shows further that
Homo primigenius in almost all his characteristics approximates
very closely to Homo sapiens, i.e. that there is an unbroken line
of development leading from Homo primigenius, through the
later Alluvial Homo sapiens fossilis, to Homo sapiens of the
1 In his table of shapes of crania (p. 357) Macnamara describes as ' closely
related ' those of which the indices differ by not more than the number 5.
2 I have quoted this sentence verbatim, because Dr. J. Bumiiller, in criticising
the previous edition of this work, in the 20 Jahrhundert, May 28, 1905, asserted
that, according to Macnamara, the Australian and Neandertal crania differed
enormously, and that I had put a false interpretation upon Macnamara's
words quoted above. That Macnamara maintains in general the descent
of man from brutes only lends additional importance to his statements on
this subject.
3 ' Der diluviale Mensch von Krapina und sein Verhaltnis zum Menschen
von Neandertal und Spy ' (Biolog. Zentralblatt, 1905, Nos. 23 and 24, pp. 805-812) ;
' Der palaolithische Mensch und seine Zeitgenossen aus dem Diluvium von
Krapina' (Mitteilungen der anthropolog.Gesellsch., Vienna, XXXIV, 1904, Parts
4 and 5).
4 Biolog. Zentralblatt, 1905, p. 810, &c.
HOMO PKIMIGENIUS 473
present day. This Is proved most clearly by the numerous
remains found at Krapina, which present many of the character-
istic features of modern man, but it is proved also by many
peculiarities of Homo primigenius that recur occasionally
at the present day. Apart from the fact that there are now
lower jaws still larger than the largest found at Krapina, we
may still meet with broad, square dental arches, badly developed
chins, and sporadically, among the Australian blacks, even
genuine supraorbital ridges (Tori supraorbitales) ; I have
moreover in my possession a modern or neolithic lower jaw
with a smooth, thick basis, such as we find In the jaws from
Spy and Krapina. We occasionally see modern jaws with too
many enamel columns near the molars, with no projection
at the chin, &c. In fact, even at the present day we can discover
a number of features which in the older Alluvial epoch were
the general characteristics of mankind, and now occur occa-
sionally by way of atavism, and on the other hand the older
Alluvial human remains sometimes present modern character-
istics. When all this is taken into account, no doubt can be
felt that there has been a continuity in evolution, proceeding
from Homo primigenius to man of our day.'
Thus far Kramberger. The bearing of his conclusions
upon the systematic classification of Homo primigenius is far
greater than his words imply. If we regard Homo primigenius
and Homo sapiens as two zoological species — and every zoolo-
gist would recognise this as a possible way of regarding them —
they now cease to be two distinct species, and appear to be
merely two races or subspecies of one and the same species, to
which, in accordance with the laws of zoological nomenclature,
we must give the name Homo sapiens. Schwalbe's Homo primi-
genius must therefore be known henceforth as Homo sapiens
primigenius, to distinguish him from Homo sapiens fossilis
and Homo sapiens recens ; he has turned out to be nothing
but an earlier race of the one true human species !
If a zoologist discovers a fossil form of wolf having certain
constant peculiarities distinguishing it from our modern
Canis lupus, he describes it as a separate species. Should he,
however, subsequently have more abundant material for
comparison at his disposal, and find then that none of the
distinguishing features are constant, nor limited to one of the
474 MODEKN BIOLOGY
two forms under observation ; should the characteristics
of the fossil wolf recur in some modern wolves, and those of
the modern wolf occur occasionally in the fossils, then the
zoologist would alter his opinion regarding the systematic
value of the two forms, and he would say : * We have here not
two distinct species, but only two races or subspecies of the
same species.' Let us adopt the same method and be serious
about the ' purely zoological classification of man,' and then
we shall acknowledge Homo primigenius to be only an older
variety of Homo sapiens.
Kramberger draws attention (p. 811) to another interesting
circumstance in the evolution of Alluvial man. He says that
the discovery of the Gaily Hill man (in England) seems to him
quite extraordinary. The strata in which these remains
were found are described as early Alluvial, whilst the remains
themselves agree very closely with those of the late Alluvial
man found at Briinn. Hence the Gaily Hill man cannot be
described as Homo primigenius, but he must be Homo sapiens
fossilis, whose remains occur in the Upper Alluvial strata, and
who resembles modern man. Kramberger infers from this
fact that, ever since the earliest Alluvial epoch, two species
of men lived in Europe, one of which, represented by the
Gaily Hill man, developed sooner and more rapidly, whilst the
other remained longer at the Homo primigenius stage, and did
not become Homo sapiens before the later Alluvial epoch.
But, as I stated above, the result of Kramberger's investiga-
tions really is that Homo primigenius was not a different
species of man, but only an earlier subspecies of Homo sapiens.
If therefore the Gaily Hill man belongs to the early Alluvial
period, we must assume that there were in Europe at
that time two contemporaneous subspecies of true human
beings.
Kramberger goes on to discuss the relationship between
Homo primigenius and the Pithecanthropus from Java (p. 812).
He believes that they belong to the same period, and that as
early as the Pliocene epoch the genera Pithecanthropus and
Homo were distinct. This is only hypothesis, and it cannot
be proved, as we have no human remains of the Tertiary period ;
but if it is true, it precludes the possibility that the ape-man
of Java might have been an ancestor of man. Kramberger
KOLLMANN'S PYGMY THEOEY 475
does not recognise the existence of any direct relationship
between Homo primigenius and the present anthropoid apes ;
he regards the morphological resemblances between them as
nothing more than analogies.
The result of these investigations may be stated in a few
words : Homo primigenius furnishes us with no evidence
in support of the descent of man from beasts.
Schwalbe's Homo primigenius therefore began by being
the representative of a genus standing between ape and man,
then he became an ape-like species of man, and now finally
he turns out to be only an early subspecies of Homo sapiens.
His scientific fate affords fresh confirmation of the notable
words used by Schwalbe in the introduction to his work on
the early history of Man (' Vorgeschichte des Menschen,' 1904) ;
he says : ' Probably in no department of natural science is
the attempt to draw general conclusions from a number of
facts more liable to be influenced by the subjective disposition
of the student than in the early history of man. On this
subject it often happens that upon a few facts theories are
based, which are stated with so much conviction as easily
to lead those, who have no special knowledge of the subject, to
regard them as assured scientific certainties.'
The conflicting character of many of the theories on the
history of mankind, which various upholders of the doctrine of
descent have propounded, is well illustrated by Kollmann's
' Pygmy theory.' l He believes that the tall races are the
descendants of pygmies. He does not regard Homo primi-
genius as a distinct species, but only as an offshoot from the
tall stock. Kollmann does not think that the Pithecanthropus
has any connexion with the descent of man, being far too
large an ape to have been the ancestor of a human race of
dwarf. In his opinion only little Tertiary apes, that walked
upright and possessed a high crown to their head, could have
been our nearest relatives in the history of our race, but un-
fortunately there is no evidence whatever to show that these
1 J. Kollmann, ' Die Pygmaen und ihre systematische Stellung innerhalb
des Menschengeschlechtes ' (Verhandl. der Naturforsch. Gesellsch., Bale, XVI,
1902, pp. 85-117) ; also by the same author, ' Neue Gedanken iiber das alte
Problem von der Abstammung des Menschen ' (Korrespondenzbl. der Deutschen
Anthropolog. Gesellsch. 1905, Nos. 2 and 3). Cf. also R. Weinberg, 'Die
Pygmaenfrage und die Deszendenz des Menschen ' (Biolog. Zentralblatt, 1906,
Nos. 9 and 10).
476 MODEKN BIOLOGY
hypothetical links between apes and dwarfs ever had any
existence !
We cannot now devote more space to the discussion of
Kollmann's ' Anthropogenesis ' ; l its hypothetical character
renders it useless for our purpose,
(c) Conclusions
The sum total of all these considerations amounts to this :
Natural science can tell us nothing with certainty or precision
regarding the descent of man from brute ancestors ; it is able
to offer us only a number of different and contradictory
theories, which prove on examination to have in common
nothing but the one idea that man must have come into
existence ' by natural means/ and for that reason we must
insist upon his being the descendant of beasts, although we
know absolutely nothing with certainty as to the manner
in which this hypothetical process has taken place.
It is no trifling matter to distort truth, as Haeckel and
many other supporters of the theory of descent have done in
popular lectures and works, when they speak of the descent
of man from beasts as ' an historical fact/ thus misleading an
uncritical public.2 Some light is thrown upon this so-called
4 fact ' by the pedigree of the Primates, sketched by Haeckel
in his Berlin Lectures,3 in 1905. This pedigree is a work of
pure imagination, and consists of a mixture of fictitious and
of really existing forms, the connexion between them being
also fictitious. From an imaginary remote ancestor the
Archiprimas, Haeckel traces the hypothetical forefathers of
our present Lemuridae and apes in an unbroken line, and
from a no less imaginary Archipithecus he traces the descent
of a fictitious primitive gibbon (Prothylobates atavus), who was
the forefather of a speechless primitive man (Pithecanthropus
1 Cf. Weinberg's article, to which I have already referred, in the Biolog.
Zentralblatt, 1906, p. 307^
2 Cf. e.g. Haeckel, Uber unsere gegenwdrtige Kenntnis vom Ur sprung des
Menschen, Bonn, 1899, p. 30. The English translation bears the title, The
Last Link, London, 1898, p. 76.
3 Der Kampf um den Entwicklungsgedanken, p. 99. The English translation
bears the title, Last Words on Evolution, London, 1906. The same pedigree
of the Primates, from the Archiprimas to Homo sapiens, appeared in the
previous work already mentioned, in 1899.
THE ANCESTOES OF MAN 477
alalus) who never existed ; * he in his turn was the progenitor
of Homo stupidus, the stupid man, from whom finally Homo
sapiens is descended !
If Haeckel hopes that the Homo sapiens of the present day
will accept his fantastic pedigree, he is mistaken. He might
succeed better with Homo stupidus, if the race is not yet totally
extinct.
At the Fifth International Congress of Zoologists held in
Berlin, Professor W. Branco, Director of the Geological and
Palaeontological Institute of the Berlin University, delivered
the closing address on August 16, 1901, and took as his subject
' Fossil Man.' The zoologists among his audience were anxious
to learn this competent specialist's opinion of the palaeonto-
logical evidence for the descent of man from beasts.2
Those who had expected to hear strong evidence in support
of Darwinism, must have been deeply disappointed, for Branco's
lecture was in the main a refutation of Haeckel's controversial
opinions expressed in his paper on ' The Last Link : Our
present knowledge of the Descent of Man,' read on August 26,
1898, at the Fourth International Congress of Zoologists at
Cambridge.
The following were the chief points in Branco's lecture :
In the history of our planet man appears as a genuine Homo
novus. It is possible to trace the ancestry of most "oTour
present mammals among the fossils of the Tertiary period,
but man appears suddenly in the Quaternary period, and
has no Tertiary ancestors, as far as we know. Human remains
1 Haeckel does not venture to call him Pithecanthropus erectus, because
recent research has shown that this fossil ape-man cannot serve as the missing
link.
2 The following statements are based upon the shorthand notes that I
made during the lecture. Cf. Verhandlungen des V. internationalen Zoologen-
kongr esses, Berlin, 1902, pp. 237-259. When the reports of the proceedings
of the Congress were prepared for the press, however, several of the most
important verbal remarks were somewhat modified, or rendered less emphatic.
A critic who withheld his name, writing in the Tiroler Tageblatt of April 28,
1905, in a feuilleton entitled ' Der fossile Mensch,' stated that in the report
given above of Professor Branco's remarks, the Jesuit Father Wasmann
had intentionally altered their meaning. The charge thus brought against
me is untrue. I wrote to Branco on the subject, and in a letter dated May 10,
1905, he declared that I had reported what he had said accurately on all
essential points. Fr. von Wagner, writing in the Zoologisches Zentralblatt,
1905, No. 22, p. 699 (see ' A Few Words to my Critics ' in the preface to this
present edition), calls my comments on Branco's lecture ' frivolous,' but he is, of
course, only expressing his own personal feelings.
478 MODEKN BIOLOGY
of the Tertiary period have not yet been discovered, and the
traces of human activity, which have been referred to that
period, are of a very doubtful nature, but Diluvial remains
abound. Man of the Diluvial epoch, however, appears at
once as a complete Homo sapiens. Most of the earliest human
beings possessed a cranium of which any of us might be proud.1
They had neither excessively long, ape-like arms, nor exces-
sively long, ape-like canine teeth, but were genuine men from
head to foot.2
Herr Branco regards the Neandertal skull and the Spy
skeleton as the sole exceptions known hitherto, and he might
have added that these exceptions are of too obscure and
problematical a nature to affect the statement that he had
just made. Similar exceptions occur often enough among
mankind at the present time, as K. Virchow and J. Eanke
pointed out long ago. Moreover, I have already shown in the
preceding pages that Homo primigenius, to whom Branco 's
remarks about exceptions referred, was merely an early sub-
species of man, and not in any sense a brute ancestor of Homo
sapiens.
In answer to the question : ' Who was the ancestor of
man ? ' Branco gives the following truly scientific reply :
* False ontologytells us nothing on the subject — it knows m>
ancestors_oi_^an/ This sentence contains the quintessence of
Branco's whole lecture.
We need not be surprised that the lecturer felt bound in
conclusion to add some remarks of a speculative character to
the scientific dissertation that formed the chief part of his
address. In these remarks he said that he was personally
convinced for zoological reasons, the weightiest of which was
Friedenthal's discovery of the blood-relationship between
man and the Primates, that man ought to be regarded simply
as the most highly developed animal. Branco was addressing
an audience of zoologists, most of whom were probably accus-
tomed to consider man from the purely zoological point of
1 N.B. — This remark was made before an assembly of eminent zoologists
from all parts of the world, whose crania undoubtedly displayed the highest
imaginable perfection of development.
a On this subject, cf. also J. Ranke, Der Mensch, II, pp. 482, 483, where this
statement is confirmed in detail. See also H. Obermaier, ' Les restes humaines
quaternaires dans 1'Europe centrale ' (U Anthropologie, XVI, 1905, pp. 385-410 ;
XVII, 1906, pp. 55-80).
CONCLUSION 479
view. At any rate, I should like to draw attention to the con-
trast between the genuinely scientific character of the greater
part of Branco's lecture, and the character of its conclusion,
in which he dealt with the theory of descent. In the body of
his address Branco spoke as a specialist in palaeontology,
and told us : ' We know of no ancestors of man.' At its
end, where he was no longer speaking as a specialist, he weakened
this declaration by adding : ' but nevertheless, looking at
man from the purely zoological point of view, we must believe
him to be descended from apes.'
In the afternoon of August 14, 1901, those who were taking
part in the Fifth International Congress of zoologists drove
in an almost interminable procession from the Parliament
House, where they had their meetings, to visit the Berlin Zoolo-
gical Gardens, and, as the carriages reached the entrance to
the Gardens, the bells of the Kaiser Wilhelm Memorial Church
began to toll solemnly in honour of the Empress Frederic,
who had just died. Accidentally, therefore, the procession of
zoologists was heralded by the sound of a muffled peal, and
the sound under these circumstances made a very melancholy
impression upon me. It seemed as if the bells were tolling
for the death of the Christian cosmogony before the triumphant
advance of zoology. Yes, if that purely zoological way of
regarding man as nothing more than a highly developed animal
is ever generally accepted, there will be no possibility of saving
Christianity and the whole modern civilisation that is based
upon it. The new cosmogony, upon which the social demo-
crats are even now fixing their longing eyes, will be the unre-
strained egoism of higher animals, whose social order stands
upon purely brute foundations, and recognises no God, no im-
mortality, and no rewards beyond the grave] When this~is
the accepted view of life, may God have_mercy upon mankmcT!
But let us nope that zoologists, who think in a truly scientific
manner, will see, before it is too late, that the purely zoological
way of regarding man takes account only of the lower part of
him, and that therefore it is an absolutely mistaken proceeding
to apply the theory of descent to him without reserve.
On the occasion of our visit to the Zoological Gardens, to
which I referred above, we were met at the entrance by an
attendant with two young chimpanzees on his arm, who
480 MODEEN BIOLOGY
were to welcome us as comrades. The two little apes grinned
at us with cheerful confidence, as if they were fully convinced
that we believed in the theory of evolution, and would like
to invite us to shake hands in recognition of the bond existing
between us. But I thought to myself : 'No, my dear little
creatures, thank God, we have not yet come to that ! '
I may therefore conclude this examination of the evidence
hitherto adduced in support of the descent of man from
beasts, by quoting a sentence from J. Beinke : l ' The only
statement, consistent with her dignity, that science can make.
is to say that she Jmows nothing about the origin of man.'
1 ' Der gegenwartige Stand der Abstammungslehre ' (Der Tiirmer, V,
October, 1902, Part I, p. 13).
CHAPTER XII
CONCLUSION
The rock of the Christian cosmogony amidst the waves of the fluctuating
systems evolved by human science (p. 481).
The storms at the base of the rock three hundred years ago, and at the present
time (p. 481).
The rock never can be overthrown by the tempests, because no real contra-
diction between knowledge and faith can ever exist (p. 483).
THE universe may be regarded as a vast ocean having in its
midst a mighty rock that has stood there for well-nigh two
thousand years. On its summit rises a Gothic cathedral,
towering up towards heaven, and within it millions of ship-
wrecked travellers have found safety. At the foot of the rock
surges the sea ; the waves sometimes gently lap it, as they
play about its base, but at other times they dash wildly against
it, and threaten to sweep both the rock and the cathedral
away into the deep.
This rock in the sea is the Christian cosmogony upon which
the Church of Christ is founded, with her divine revelation and
divine teaching, whereby men may be saved. The waves that
ebb and flow at the foot of the rock are the ever-changing
systems evolved by human knowledge.
Some three hundred years ago a furious storm raged round
the rock, for many centuries a peaceful wave had washed its base,
seeming to be so calm and friendly as almost to be inseparable
from it. Suddenly a mighty tempest arose, and after a conflict
of a hundred years a new wave succeeded in driving away its
quiet predecessor. The dwellers on the rock trembled at the
uproar of the elements ; they feared that the rock itself must
fall, if the wave that had for so long seemed its inseparable
ally were hurled back into the deep, but their fears were
groundless. The old wave disappeared, but the rock stood
firm, and the new wave, which had at first lashed it in anger,
gradually sank to rest, and now rests peacefully at its foot.
The tempest, that I have just described, was the struggle
481 2 i
482 MODEEN BIOLOGY
between the Ptolemaic and the Copernican systems. The
former erroneously made our little earth the centre of the
universe, with sun, moon, and stars revolving about it. The
latter deprived the earth of her central position, assigned to
her the moon as her sole satellite, and regarded her as merely
one of many planets belonging to one of many suns ; reduced
her, in fact, to the position of a mere atom in the universe.
Many pious minds were overwhelmed with fear lest the rock
of Christianity should lose its equilibrium, if the earth really
revolved about the sun, but that it does so disturbs no one at
the present time. Christianity proved to be far too strong
and far too great to be affected by the new theory of the
universe. And now this very theory, that once appeared so
dangerous, rests peacefully at the base of the ancient rock and
even plays about its foundations.
To-day no educated man doubts that the Copernican
system is perfectly compatible with Christianity.
Three hundred years passed, and about fifty years ago
another tempest arose. The waves of the theory of perman-
ence had long been quietly lapping the rock, and again it seemed
as if they were inseparable from it, and many of the inhabitants
of the island believed these waves to be indispensable to their
very existence, and thought that if they had to give place to
other, stronger waves, the downfall of the rock must inevitably
follow, and with it the Church built upon its summit must
perish likewise. And the new wave came, and like a deluge
the doctrine of evolution, originating in England, burst upon
the theory of permanence ; the conflict between them is still
raging, but we can already see what will be its issue ; the old
wave must pass away and the new wave will remain, until it
too has to give place to a stronger.
But the dwellers on the rock need feel no fear ; even if the
old wave passes away, the rock will stand firm until the dawn
of eternity.
On the white crests of the waves that still angrily threaten
even the summit of the rock are thousands of tiny bubbles,
that seem to fancy themselves about to destroy both rock and
Church. They represent modern unbelief, and they imagine
that the theory of evolution furnishes them with the best
possible weapon against Christianity.
THE KOCK OP CHRISTIANITY 483
These bubbles, however, deceive themselves. Ere now
far more powerful drops have attempted to overthrow the
rock, but they have all gone their way and accomplished
nothing ; and these new bubbles, eager as they are for the
battle, will fare likewise. It may well be that ere long the
new wave of the evolution theory will lower its proud crest, and
sink peacefully to rest at the foot of the ancient rock.
The tide of human knowledge is in no sense a natural
enemy of the Christian cosmogony. On the contrary, it is
naturally the friend of Christianity, for human knowledge
proceeds from the same divine wisdom that created also the
rock and the mighty Church upon it.
Between natural knowledge and supernatural revelation
no real contradiction is possible, because both have their
origin in the same divine Spirit. This fact was denned and
clearly stated by the Vatican Council,1 and the late Pope,
Leo XIII, discussed it more in detail in his encyclical ' Aeterni
Patris ' (August 4, 1879).
If, therefore, the powers of darkness stir up angry tempests
which hurl the waves of human knowledge against the rock of
the Faith, the waves are not to blame, but rather the powers
that make use of them. These storms will never overthrow
the rock of Christ : Non praevalebunt adversus petram !
Whether the waves ebb or flow about its foot, whether the
water is calm as a mirror or is lashed mountain-high by hostile
forces — the rock of Christianity will stand firm and unshaken
to the end of time !
1 Constitutio dogmatica de Fide catholica, c. 4, ' De fide et ratione.'
2 i 2
APPENDIX
INNSBEUCK LECTURES
INTRODUCTION
AT the request of the students' association of Innsbruck University
I undertook to deliver some lectures there in the middle of October
1909 on the subject of evolution, but I had no idea that they
would arouse so much interest in the capital of my native land, as
proved to be the case.
According to my usual practice, I spoke extempore, having
merely noted down a few headings immediately before each lecture,
and I was therefore obliged to write a short summary of the first
two lectures for the Allgemeiner Tiroler Anzeiger on the morning
following their delivery in the hall of the Austria-Haus. The
third lecture was given in the Town Hall, before a far larger audience,
and on this occasion there were fortunately six shorthand- writers
present ; I was so completely exhausted by over-exertion that it
would have been impossible for me on the day after that lecture
to remember what I had said. . . .
As the lectures appeared first in the Allgemeiner Tiroler An-
zeiger, and as the printers of that paper use rotary presses, no
subsequent corrections could be made in the text, and all that I
could do was to add a few notes here and there. This explains why
the newspaper articles have been reprinted almost unaltered. The
first lecture is reproduced in a much abbreviated form, the second
somewhat more fully, and the third, having been taken down in
shorthand, appears in extenso, in fact I have expanded the last
section, in which my remarks were much condensed, owing to the
lateness of the hour when I concluded my lecture.
Some few repetitions were unavoidable, as, at the beginning
of the third lecture, I was obliged to recapitulate what I had said
on the preceding evenings for the benefit of many people present,
who had been unable to find room in the Austria-Haus. This
recapitulation, however, is by no means superfluous, as it contains
remarks suggesting new points of view for considering the doctrine
of descent as a scientific theory.
* * * * *
My object in publishing these lectures, and thus rendering them
accessible to a wider circle of readers, is to supply university students
484
INTKODUCTION . 485
with a short sketch, of the scientific doctrine of evolution and its
bearing upon monism and Christianity respectively.
The students at Innsbruck in particular are requested to regard
this work as a token of my grateful acknowledgment of their
efforts to obtain truly scientific information, and I beg them to
bear in mind the words with which I concluded my third lecture :
The only true monism is that of Christianity ; viz. there is but one
eternal God and one eternal truth !
If these lectures serve to confirm and strengthen one among
thousands of students in his faith as a Christian, I shall consider
myself richly rewarded for all the mental and physical fatigue that
they have involved. . . .
ERICH WASMANN, S.J,
LUXEMBURG,
BELLEVUE.
First Lecture, delivered in the Austria-Haus at Innsbruck
on Thursday, October 14, 1909
THE THEORY OF EVOLUTION AND THE
CHRISTIAN COSMOGONY
THE lecturer began by explaining why he had felt particular pleasure in
accepting the invitation to address the students at the university of Inns-
bruck. Trustworthy information regarding the true value of the theory
of evolution and its bearing upon the Christian view of the universe is
most necessary in academic circles, as supplying a means of resisting
the attacks of monism upon Christianity, since monism employs the doc-
trine of evolution as ' heavy artillery ' in the strife. The lecturer referred
to the discussion aroused in February 1907 by his Berlin lectures on the
theory of evolution, and quoted one of his opponents to prove that the
freedom to express scientific opinions was jeopardised by the tyranny of
' Monistic beliefs.' ' Free men ought not,' he said, ' to tolerate such
tyranny, least of all in the Tyrol.'
The speaker then proceeded to outline the contents of the lectures
that he was about to deliver. In the first he proposed to deal with the
doctrine of evolution as a theory and hypothesis in natural science, and
with the subject-matter of this theory of evolution, the evidence supporting
it and its limitations. The various causes of evolution would be discussed
in the next lecture.
1. What is the subject-matter of the doctrine of evolution or descent
as a scientific hypothesis and theory ? l
Its subject is the investigation of the evolution of plants and animals,
from the first appearance of life upon the world to the present time. Man
came upon the stage of life as an epigone, and therefore it is only with
difficulty that he can decipher the records of life upon our earth, tracing
them in fossil remains of creatures long extinct, and comparing them with
the organic forms of the present. It is plain that the theory of evolution
cannot be an empirical science ; it is only a structure built up of hypotheses
for which, both individually and collectively, nothing more than probability
can be claimed. To speak of descent from one or other hypothetical
ancestor as an * historical fact,' as Haeckel for instance does in discussing
the evolution of man, is wilfully to deceive an uncritical public.
The scientific doctrine of evolution is not concerned with explaining
the origin of life from inorganic matter. It assumes the existence of life,
and only seeks to ascertain how the living forms of the present have been
evolved from those of the past. It has therefore nothing to do with the
1 For a more complete answer to this question see pp. 267, &c., and The
Problem of Evolution (Lectures delivered at Berlin), pp. 6, &c.
486
THE THEORY OF EVOLUTION 487
question of spontaneous generation, nor does it in any way belong to the
theory of evolution to decide whether our present forms of animal and
vegetable life originated in one single primitive cell, or in a few such cells.
It is true that monism maintains a monophyletic evolution of all forms
from one common origin to be alone truly scientific, and declares, with
great assurance, that it is impossible to accept a polyphyletic evolution
from several primitive forms, and that, whoever accepts it, does so under
theological influence. But this monistic opinion is not free from pre-
suppositions, and is, on the contrary, thoroughly one-sided and involved
in biassed assumptions. Which view we ought to take of the phylogeny
of the organic world is not to be decided by the so-called postulates of
monism, but solely by a careful examination of facts supplying us with
indications. The scientific doctrine of evolution is not a question of
dogmas but of facts.
And what do facts tell us regarding the evolution of organic beings ?
This brings us to the second point :
2. Actual evidence in support of the theory of evolution.
This is of two kinds, direct and indirect ; the former is naturally very
scanty and is derived from relatively slight modifications in species, for
the hypothetical evolution of organisms is a process that terminated in
some remote past, and only traces of it can be observed by us, who are
but newcomers on the earth. There are, however, traces of the formation
of new species being actually in progress, or having taken place recently,
if we use the word in its geological signification. In illustration, the
lecturer referred to instances from his own special department of research,
and mentioned particularly the evolution of species within the genus of
Dinarda beetles, and the transformation of the guests of East Indian and
African wandering ants into termite inquilines, the change in habits
having given rise to new species.
Far more abundant is the indirect or circumstantial evidence in
support of a race-evolution of animals and plants. It is derived from
palaeontology, comparative morphology, comparative biology, and com-
parative ontogeny, or the history of individual development. The
lecturer discussed these sources of evidence singly, and illustrated them by
a number of instances, taken chiefly from his own branch of biology. In
addition to the so-called ' permanent types,' which have remained unaltered
for long geological periods, palaeontology shows us also certain types that
are liable to change, and in the course of time new species, genera, and
families have been formed amongst them. Comparative morphology, in
conjunction with comparative biology, enables us to recognise the wonder-
ful ' adaptation characteristics,' possessed by the inquilines of ants and
termites, as the result of a natural process of evolution, and in the
second part of the lecture a number of photographs were shown
illustrating this statement. The lecturer showed how comparative
biology could account for the growth of the slave-making instinct in ants,
and this point too was illustrated by photographs. In speaking of com-
parative ontogeny, he carefully distinguished the true and the false ele-
ments of the so-called * biogenetic law.' The greatest authorities (Oskar
Her twig, Keibel, &c.) have recently shown that it is impossible to
maintain this law to be universally applicable, but nevertheless in many
cases the individual ontogeny of an animal furnishes valuable suggestions
for the investigation of its phylogeny. This remark is borne out by the
appearance of teeth in the embryo of the whalebone whale, and by the
488 INNSBEUCK LECTURES
development, from formations really resembling wings, of the peculiar
appendages on the thorax of the termitophile genus of fly, known as
Termitoxenia.
3. The lecturer next proceeded to discuss the limitations of the theory
of evolution. What is proved by all the above-mentioned evidence,
direct and indirect ? Does it show that the whole animal and vegetable
kingdom has developed from one, or even from a few primitive cells,
and that the evolution has been monophyletic ? No ; the advance of
phylogenetic research tends to destroy this pleasing fiction, and facts
"\ Teally suggest that the development of both the animal and the vegetable
kingdoms has been polyphyletic, i.e. that there have always been many
distinct kinds of animals and plants. The names were mentioned of many
eminent palaeontologists, botanists, and zoologists of the present day
who share the lecturer's opinions on this subject.
The idea of the ' natural species ' in its bearing upon our acceptance
of polyphyletic evolution was the next point discussed.1
A natural species consists of the members of one series of forms, con-
nected phylogenetically by descent. This definition of the natural species
was given by Neumayr many years ago, and so it is by no means an
invention of theologians, as the monists constantly assert. It is true that
Neumayr spoke of ' palaeontological,' and not of * natural ' species, but
he meant exactly the same thing.
At the present day science is not in a position to determine how many
such natural species or phylogenetic series we must assume to exist, nor
the extent of each series, nor the nature of the primitive forms which
gave rise to the natural species. We may, however, confidently expect
that more light will be thrown upon these subjects by future research,
and this advance in the scientific doctrine of evolution need cause no alarm
to theologians nor to any who believe in Christianity. Scientific progress
can never contradict our infinitely exalted Christian cosmogony, which
is absolutely independent of the fluctuating theories of mankind. The
x- theory of evolution does not clash with the Christian dogma of creation,
But completes it in the most beautiful manner. A God who could create
a living world capable of evolution is immeasurably greater and higher
in His wisdom and power than a God who could only set all living creatures
/ jn the world as fixed, unalterable automata. The greatest intellects of
the Middle Ages and of antiquity, such as St. Thomas Aquinas and St.
Augustine, perceived and expressed this truth, and therefore we may
calmly continue to accept the dignified account of the Creation : ' In
\ fhe beginning God created the heaven and the earth.'
*****
After a short pause a series of about fifty lantern slides was shown.
They illustrated the lecturer's particular department of research, and were
all original photographs of ants or of inquilines living among ants and
termites.
1 See pp. 296, &c., and The Problem of Evolution, p. 15.
DAKW1NISM 489
Second Lecture, delivered in the Austria- Haus at Innsbruck
on Saturday, October 16, 1909
DARWINISM AND THE THEORY OF EVOLUTION
WE constantly hear most conflicting opinions expressed on the
subject of Darwinism. Some maintain that it is dead and buried,
others that it is in vigorous health. Some regard it as the outcome
of atheism, others as an acceptable scientific theory. One and the
same man, Ernst Haeckel, has spoken in very contradictory terms
about Darwinism. At one time he declared it to be the ' heavy
artillery ' of monism nfits intellectual struggle with Christianity,
afterwards he actually discovered a ' Darwinian Jesuit,' and boldly
asserted that the Jesuit Order and the whole Catholic Church had
in 1904 gone over to Darwinism. In order to counteract this
dangerous flank attack, which threatened the chief stronghold of
monism, Haeckel himself gave some public lectures on the subject
of evolution in Berlin in 1905. These circumstances add a peculiar
interest to the question : ' What are we to think about
Darwinism ? ' It is a very complicated question, and unless we
carefully distinguish the various meanings of the word Darwinism,
we shall be unable to answer it satisfactorily. Here, as ever, clear
comprehension is the mother of truth.
Let us therefore consider Darwinism : (1) From the point of view
of natural science ; (2) In the sense in which it is used in popular
science, and especially in the signification given it by Haeckel and
the monists.
1. DARWINISM IN REFERENCE TO NATURAL SCIENCE
Darwinism in this sense is the particular form of the theory of
descent which was originated by Charles Darwin, and called by
him the ' Theory of Natural Selection.' It differs from the other
forms of the theory of descent in the causes and mode which it
assigns to evolution. To-day's lecture on Darwinism is therefore,
strictly speaking, a continuation of my remarks the day before
yesterday upon the doctrine of evolution as a scientific hypothesis
and theory. On that occasion I discussed its nature, the evidence
supporting it and its limitations ; to-day, I have to deal with the
causes of evolution and its external manifestation. In this way we
shall arrive at a just estimate of Darwinism, from the point of view
of natural science.
That Darwinism is not the only doctrine of evolution, but merely
one of several such doctrines, and that the name Darwinism ought
properly to be applied only to Charles Darwin's theory of natural
selection are facts universally acknowledged by scientific men.
490 INNSBKUCK LECTUKES
Oskar Hertwig was perfectly right in 1900 when he said emphatically
with reference to Huxley : ' If Darwinism were swept away, the
theory of evolution would stand as it did.' Even Ernst Haeckel in
his Berlin lectures in 1905 admitted at last that Darwinism, strictly
speaking, was nothing but Darwin's theory of natural selection,
although in the course of the same lectures he proceeded to confuse
Darwinism with the theory of evolution in his usual fashion.
Darwinism, therefore, is that particular form of the theory of
evolution propounded by Charles Darwin in 1859, and by Alfred
Russel Wallace at almost the same time, which assumes, in the
first place, that natural selection is, if not the sole, at least the
chief cause of evolution ; meaning thereby that only the fittest
individuals survive in the struggle for existence, and, in the second
place, that evolution consists of a gradual accumulation of imper-
ceptibly slight ' fluctuating variations ' continued through innumer-
able generations. According to this theory, if we regard natural
selection as the chief factor in evolution, enormous periods of
time are necessary for one species of animal to be evolved from
another.
The lecturer went on to discuss Darwin's Natural Selection more in
detail, showing that it was based upon a comparison with the artificial
selection employed by man in breeding his domestic animals, which has
been so successful in producing new breeds. But in the case of natural
selection there is no intelligent breeder directing the process, it secures
merely the survival of the fittest, i.e. of the forms best capable of standing
their ground in the struggle for existence. It is therefore purely a negative
factor, producing nothing new, and having as material for selection only
already existing variations. Darwin did not investigate the origin of the
beneficial variations, and tacitly assumed that a living organism was by
nature capable of evolution. In his opinion the capacity for variation
was indefinite arid unlimited. It seemed, therefore, to him a matter of
chance whether beneficial variations occurred at all, and only by chance
again could they be transmitted to succeeding generations. Viewed in
this way, Darwin's theory of selection appears to be ultimately a theory
of chance.
Darwin was not, however, so extreme a Darwinist as many
of his followers, e.g. as Weismann, who, as chief representative of
the so-called 'New Darwinism,' proclaimed the all-powerfulness
of natural selection. Darwin himself on occasion admitted the
claims of the 'Nature of the organism,' and did not deny its capacity
for adaptation and the possibility of the transmission of properties
acquired by an individual. He accepted also Cuvier's principle
of correlation. Nevertheless, natural selection is, and remains, the
chief factor of all race-evolution, according to his theory.
What must we, as students of natural science, think of this
form of Darwinism ? It is thoroughly unsatisfactory, for it accounts
neither for the cause nor for the manner of evolution. Natural
selection is not a sufficient cause for evolution, because it leaves
DAEWINISM
491
the origin of what is beneficial unexplained, and is able only to
account for the extirpation of what is not beneficial. It is a purely
negative factor, and de Vries has very aptly compared it with
a sieve, that sifts out the unfit, but does not explain the origin of
the fit. It may be compared also with a strict examiner, who
rejects the badly prepared students, but the reasons why the well
prepared candidates pass the examination are to be sought in
their knowledge of the subjects set, which the examiner does not
invent, but in which he tests others. Again, natural selection
resembles a gardener's boy pulling up weeds. His activity is
purely negative, and presupposes the existence of the gardener, who
has planted in the earth the plants that are to remain untouched.
Pauly says that natural selection is like von Scheffel's * Haus-
knecht aus dem Nubierland,' who turns out of the Black Whale
in Ascalon any guest unable to pay his bill, but cannot supply
money for payment ; all he can do is to keep the place clear of
unwelcome intruders.
There are other reasons too against accepting the theory of
natural selection. It can offer no explanation of biologically
indifferent characteristics of animals and plants, although these
are of far more frequent occurrence as distinguishing species than
the biologically beneficial properties. ... By assuming that evolu-
tion is a process involving an extremely slow accumulation of very
slight changes, the theory of natural selection requires, for the
evolution of any one species from another, immeasurable periods of
time, which are incompatible with geology. It demands also that
in the strata containing fossil remains of extinct organisms we
should regularly find series of gradual variations, and not sharply
distinguished species. Paleontology, however, shows us the actual
existence of a contrary state of affairs. Series of very slight varia-
tions are an extremely rare exception, not the rule. To try to
account for this fact by referring to the defective condition of
palseontological records is a hopeless attempt, in view of the positive
progress made by modern study of fossils.
We must, therefore, come to the conclusion that we cannot
regard natural selection as the chief factor in evolution, for it is
scientifically impossible to do so. Must the theory be rejected
altogether ?
It is an incontestable fact that Hans Driesch and many other
scientific opponents of Darwinism have rejected it. Driesch
called Plate's attempt to save it ' a funeral oration,' uttered on
the principle de mortuis nil nisi bonum. Dennert, too, considers that
he has already stood by the deathbed of Darwinism and witnessed
its last agony. I do not, however, believe this. By far the majority
of botanists agreed long ago to set a very modest and greatly modified
value upon the principle of selection, and now modern zoologists are
doing the same, but they do not wholly reject it, and in my opinion
theirs is the only correct attitude towards it. As a subordinate
492 INNSBKUCK LECTURES
factor among others of much greater importance, Darwin's natural
selection still demands recognition, and will continue to do so.
The lecturer illustrated this remark by an interesting example of the
hypothetical evolution of the slave-making instinct in ants. The wonder-
ful instinct, prompting them to steal the worker pupae of other species and
bring them up as their assistants, is not due to natural selection, as Darwin
assumed, but originated in a much simpler, shorter, and more natural
manner. It is the result of the establishment by the females of dependent
colonies, in conjunction with an alteration in the previous mode of nourish-
ment among the workers. Climatic changes would cause changes in the
vegetation, forest flora would be replaced by that of the steppes, and thus
ants might be forced to live exclusively on other insects, and preferably
on the pupae of other kinds of ants. Of the stolen pupae only those of one
particular species were allowed to live, because the females of the robbers
had originally founded their colonies by the aid of ants of this kind ;
hence the latter became the slaves of the former. Thenceforth natural
selection might promote the further development of a slave-keeping
instinct in the robber-ants (though it would do so only as an exterior
subsidiary factor) until this development reached its culminating point,
and then degeneration of the slave- keeping instinct began, and led to the
lowest state of social parasitism in which the masters are mere parasites
dependent upon their former slaves. Such degeneration of the slave-
making instinct must lead finally to the extinction of the original masters,
and to the dying out of the species. This process was due to interior
causes, and continued, although it ultimately proved most destructive
to the species ; natural selection was unable to check it, and proved in
this case powerless and not all-powerful.
The lecturer went on to discuss the other factors of evolution that
must be assumed to co-operate in the evolution of a race. The chief
factors in the evolution both of a race and of an individual are the interior
organic and psychical laws governing the development of organisms.
He established the existence of these laws and answered the objections
raised by monists and materialists. The working of these interior laws
of development is seen, he said, in the capacity for reaction possessed by
the simplest little mass of protoplasm, for upon this beneficial capacity
for reaction depend the organic functions of nutrition, movement, growth
and propagation. Unless we assume these interior factors of development
to exist, all development of organic life is impossible. Wasmann's oppo-
nents in Berlin could not disprove this statement at the famous discussion
on the evening of February 18, 1907 ; in fact, the eleventh speaker even
expressed himself in favour of admitting the existence of these interior
factors. When Plate and other opponents of teleology thought they could
get rid of these laws by calling them ' mystical,' they were labouring under
a false impression due to their absolute failure to understand the nature
of these factors. These interior laws of development ought not to be
regarded as working automatically like a clock, but as acting reciprocally
with the exterior impelling causes and stimuli of evolution. For this
reason we cannot accept, in its extreme form, Eimer's ' Orthogenesis,'
a theory maintaining that evolution proceeds in an uninterrupted course
from interior causes.
The lecturer then referred to adaptation. The purely passive and
mechanical adaptation of Darwinism, consisting merely of the elimination
DAEWINISM 493
of the unfit, is absolutely unsatisfactory as a cause of evolution. Over
and above it we need what is of much greater importance, viz. an active and
direct adaptation of the organism to the influences of the world around it.
Lamarck and Geoffroy St. Hilaire established the principles of direct
adaptation early in last century, and these same principles have found their
modern expression in such phrases as ' La fonction cree 1'organe,' &c.
Allusion was made to the close connexion between Lamarckism 1 and
the thoroughly sound Neovitalism of Hans Driesch and Reinke, and also
to Neo-Lamarckism, which in Pauly and France has assumed the form of
so-called Psycho-Lamarckism.
The lecturer showed how far these views were justifiable, inasmuch
as they recognised in living organisms interior tendencies to evolution ;
but he criticised very sharply the outgrowths of Psycho-Lamarckism,
especially in France's works. France is unable to avoid acknowledging
the existence of a teleological principle of interior design, which must
ultimately lead to the recognition of a thinking and intelligent cause,
such as Christian philosophy regards as effecting the creation, at the begin-
ning of the evolution of organic life. He, however, prefers to make
an unsuccessful and unscientific attempt to represent each cell in a living
organism as a diminutive creator endowed with reason. In this way he
has placed plant-life on a level with human life in a most uncritical fashion,
but nevertheless he has not succeeded in explaining the existing unity in
the development of plants and animals from that aggregate of ' cell-souls.'
This Psycho-Lamarckism is worse than the most extreme Darwinism from
the scientific point of view.
The lecturer discussed briefly the question of the transmission of
acquired properties, and the relations between germ-plasm and somatic
plasm. He stated any evolution of instinct in the animal kingdom to be,
in his opinion, inconceivable, unless this transmission is possible. The
difficulties formerly raised against the possibility of inheriting individually
acquired properties had, he said, in the case of ants been happily removed
by recent investigations.
He went on to speak of the important bearing of climatic changes upon
the evolution of species and of their instincts, illustrating his views by
instances from the development of slavery and of social parasitism
among ants, which he had described more fully, in the Biologisches
ZentraMatt for 1909.
The other factors of evolution were mentioned, which are noticed in
R. Wagner's ' Theory of Migration,' in Romanes and Gulick's ' Physio-
logical Selection,' in Roux's ' Histonal Selection,' and Weismann's
' Germinal Selection,' the last two having been introduced to supplement
the theory of personal, or, as Darwin called it, natural selection. The
lecturer referred also to ' Amical Selection,' a name which he himself had
used twelve years previously to designate the instinctive preference
shown by ants and termites for certain breeds of inquilines. That this
predilection was a factor in evolution had been proved by actual observa-
tions. This form of selection differs altogether from both natural and
sexual selection, and of all the forms of selection among animals it most
closely resembles the artificial breeding practised by human beings.
This part of the lecture concluded with the remark that, if the theory of
1 See also Geschichte des Lamarckismus by Prof. Dr. Adolf Wagner of Inns-
bruck (Stuttgart, 1909).
494
INNSBEUCK LECTUEES
evolution were to agree with facts, it must avoid all tendency to take a one-
sided view of the causes of evolution. Many factors invariably act
together, though their participation may vary in degree according to the
differences in the lines of evolution under consideration. As proof of this
statement, reference was made to the hypothetical evolution of three
biological types of guests entertained by ants, viz. the offensive, the
mimetic, and the symphilic types respectively, which were illustrated by
photographs in the first lecture.
A general survey of the various forms of race-evolution followed.
Darwin assumed evolution to be a very slow and gradual process, working
by means of fluctuating variations, whereas Kolliker's heterogony and
the theories of Korschinsky and de Vries require the changes to have
occurred per saltum, and Jackel's metakinesis involves a rapid alteration
of forms in the embryonic stage. Heer, Zittel, and de Vries believe periods
of change and periods of rest to have alternated in the history of organic
life, but care must be taken to avoid adopting any one of these ideas on
evolution exclusively, as, in many cases, several kinds of evolution may
be at work, sometimes in different, sometimes in one and the same line of
evolution.
2. DARWINISM IN THE WIDER AND MORE POPULAR SENSE
The word ' Darwinism ' is a genuine Proteus ; it possesses at
least four different meanings. In the first part of this lecture I
have been speaking of Darwinism in the correct, scientific sense,
viz. Darwin's theory of natural selection. Great confusion has
resulted from what we may confidently call the unscientific use
of the word in several other senses. By Darwinism people often
mean a theory of the universe based upon an absolutely uncritical
generalisation of the principle of natural selection, the struggle
for existence, that is practically identical with the old materialistic
theory of chance, which nowadays calls itself monism, in order
to hide its atheism.
A third use of Darwinism is to designate the unreserved exten-
sion to man of the theory of natural selection. This results in
degrading man to the level of brutes, and overthrows the social
order depending upon the principles of Christianity. It has
nothing further to do with the scientific evidence of the descent
of man from brutes, which I intend to examine in my next
lecture.
There is yet a fourth use of the word Darwinism, as synonymous
with the theory of evolution in general. Every one knows that
in scientific circles Darwinism and the theory of evolution are
no longer confused, but in popular language the terms still continue
to be treated as interchangeable, and great harm has been done
in this way. It was an excusable mistake fifty years ago, when.
Darwin first became prominent, and his ' Origin of Species ' revived
the memory of Lamarck's long forgotten ideas regarding evolution,
and directed men's attention to the theory of evolution itself. But
at the present day there is no excuse at all for confusing Darwinism
DAKWINISM 495
with, the theory of evolution. If the monists persist in doing so,
it is because they hope thus to propagate the Darwinian theory
of the universe in a by no means scientific, but in a thoroughly
unscientific and dishonest way. An article on the further develop-
ment of Darwinism ('Die Weiterentwicklung des Darwinismus'),
published by France among Breitenbach's ' Darwinistiche Schriften,'
is an instance of what I mean. All the recent progress made in
the scientific theory of evolution, even Neovitalism, which is
directly opposed to Darwinism, is here represented by France as
' further developments of Darwinism.' Not satisfied, however, with
thus misleading his readers, France has even ventured to falsify a
quotation from my works, in order to transform me from a supporter of
the theory of evolution into an advocate of the theory of permanence.
This unmistakable falsification was pointed out to him, but,
instead of correcting it, he actually repeated it once more. Such
a proceeding is not merely unscientific, but absolutely dishonest.
Plate's line of action is not much better, for in one of his more
recent publications he classes Reinke and myself among the oppo-
nents of the theory of evolution, although he knows perfectly well
that such a statement is simply a falsehood. If the monists are
forced to have recourse to such means as these in their efforts
to ' enlighten ' the people, and to gain adherents for their new
monistic cosmogony, they are much to be pitied.
In what relation does Darwinism stand to Christian philosophy ?
Christianity has nothing to fear from scientific Darwinism. More
than twenty years have passed since Haeckel triumphantly declared
that Darwin's theory of natural selection supplied an explanation
of finality in nature, and enabled men to do without a ' wise Creator,'
but this declaration has proved to be nothing but bombast, and at
the present time no one takes it seriously. The Darwinian cos-
mogony, however, which is based upon a thoroughly unscientific
generalisation of the theory of natural selection, has, under the form
of Haeckel' s monism, revealed itself as barren materialism and
atheism, and I shall have to say more about it in the third lecture.
Men of science in years to come will honour Charles Darwin's
memory more highly than Haeckel's, for the latter popularised
scientific Darwinism with the express purpose of using it as a
'weapon against Christianity. In so doing he has diminished
rather than increased the scientific reputation of the theory of
evolution. Allow me to conclude this lecture with the noble
words written by Charles Darwin at the end of his ' Origin of
Species ' : ' There is grandeur in this view of life, with its several
powers, having been originally breathed by the Creator into a
few forms or into one ; and that, whilst this planet has gone cycling
on according to the fixed law of gravity, from so simple a beginning
endless forms most beautiful and most wonderful have been, and
are being, evolved.'
496 INNSBEUCK LECTURES
Third Lecture, delivered on October 18, 1909, in the
Town Hall at Innsbruck
THE DESCENT OF MAN, HAECKEL'S THEOEIES, MONISM
LADIES AND GENTLEMEN, —
I must begin by thanking you for the extremely hearty
welcome that you have given me in Innsbruck. It is all the more
pleasant to me because I am myself a native of South Tyrol, I may
even say a neighbour of Andreas Hofer's.
As the time allotted for my lecture is very short, although the
subject with which I have to deal could receive adequate treatment
only in a course of lectures, I must be as brief as possible. My
programme is as follows : —
1. Summary of the two previous lectures, rendered necessary by
the presence this evening of an audience two or three times
as large as on the first night.
2. Display of the most important photographs shown on the
previous evenings, and illustrating from my own depart-
ment my remarks on direct and indirect evidence for the
theory of evolution.
3. Discussion of the question : What evidence does natural
science furnish of the descent of man from brutes ?
4. After a short interval I shall show you some more photographs
belonging to the morphological and palseontological sides
of the argument ; and here again I must limit myself to
what is most indispensable.
5. In the fifth part I shall have to speak of Haeckel, and throw
some sidelights upon his manner of dealing with anthro-
pological problems, especially with reference to the phylogeny
of man.
6. In conclusion I shall examine with what right monism claims
to have replaced the Christian cosmogony by a new theory
of the universe, based chiefly upon scientific principles of
evolution.
7. Lastly, there will be a discussion, in which all are invited
to take part whose scientific attainments enable them to
form an opinion on these questions. I shall avail myself
of the opportunity, given me by the discussion, to elucidate
two points that seem to me particularly important. All
personal feeling shall be set aside, and I intend to speak
simply in the interests of truth.
1. Let us begin by reviewing shortly the results of the two
previous lectures. My subject throughout is the theory of evolution
and the Christian cosmogony, but I am dealing with the latter only in
as far as it is necessary to do so, in order to remove the alleged
contradictions between the theory of evolution and Christianity.
In the first lecture I spoke of the doctrine of evolution as a scientific
hypothesis and theory, considering first its nature, secondly the
THE DESCENT OF MAN 497
evidence supporting it, and thirdly its limitations. In the second
lecture I discussed the causes of race-evolution, and the particular
forms which evolution is supposed by the advocates of different
theories to have assumed. I called this lecture ' Darwinism and
the theory of evolution,' simply because Darwinism differs from all
other theories in the causes and form that it assigns to evolution ?
What are we to think of the doctrine of evolution as a scientific
hypothesis and theory ? What really is the theory of evolution ?
It maintains that organic species may be related to one another
in virtue of having a common origin, and so they can be arranged
in definite lines of descent. This theory contradicts that of per-
manence, which regards the organic species as unchanging, and
received its present form from Ray, Linnseus, and Cuvier. The
scientific foundations of the evolution theory were laid in 1809
by Lamarck, in his ' Philosophic zoologique,' and in 1859 Darwin
gave it a new form in his ' Origin of Species,' so that this particular
form is called Darwinism after him.
It is not the task of the theory of evolution to account for the
origin of life, but only to explain the further development of life,
taking existing facts as its points d'appui. We have, therefore,
nothing to do now with the origin of life, and from this definition
of the theory it follows that it is not essential to it to trace back
all animals and plants to a single primitive cell, nor to assume a
common ancestor for all animals and all plants respectively.
Whether we are to assume there to have been one or many lines of
descent, or, in other words, whether we are to regard evolution as
monophyletic or polyphyletic, is a subordinate question, forming
no essential part of the theory of evolution. Such questions
cannot be answered by the postulates of monism, because the
theory of descent, being a scientific hypothesis and theory, has to
do with facts and not with dogmas. This may suffice as a short
account of what the theory of evolution really is, and it may also
remove certain misunderstandings which have crept in, and obscured
the definition of the theory, chiefly in consequence of monistic
misrepresentations.
We have next to consider what evidence there is for the theory
of evolution. What justifies us in believing that any evolution of
organic species has occurred among animals and plants ? Men
occupy a difficult position with regard to this question, for we are
epigoni, appearing at the close of a long process of evolution, begun,
perhaps, thousands or even millions of years ago ; it is impossible
to fix its duration. We are obliged to gather fossil traces of bygone
evolution from geological strata, and to compare these palseonto-
logical data with things existing at the present day, in order to
connect kindred species in genealogical series.
From its very nature our evidence is circumstantial rather than
direct ; to discover direct proofs of the theory of evolution" in facts
of the present time, or of the not very remote past, is a very difficult
2 K
498 INNSBKUCK LECTURES
task, because the hypothetical evolution of the organic world belongs
to the most distant ages, in comparison with which thousands of
years, as we reckon them, are but a fraction of a second. It follows,
obviously, that the theory of evolution can never become an absolute
fact, or a branch of empirical science, the results of which can be
tested directly by observation and experiments. It never can be
more than a structure built up of hypotheses, i.e. of more or less
probable assumptions. Indirect evidence in support of it may be
derived from various sources.
In the first place we have the testimony of palaeontology, or, as
Steinmann calls it, historical evidence. We must seek the fossils
preserved in various strata, and compare them with the still existing
forms of animals and plants, in order to discover the relation in
which they stand to one another and to our present species.
In the second place we must take into account the results of
comparative morphology, which has made great progress in the
last few years. We must compare the various organs and systems
of organs in animals with one another, and note their points of
similarity and of difference, and try to ascertain how far they suggest
community of origin. It is true that we must proceed very
cautiously, and avoid confusing the so-called phenomena of con-
vergence with phylogenetic resemblances. The former, in conse-
quence of similarity in the mode of life and in the conditions for
adaptation, may produce forms showing marked likeness in animals
of very different origin. It is safe to draw conclusions from this
source only when the evidence derived from morphology agrees with
the testimony of palaeontology and of comparative embryology.
Comparative biology, by throwing light on the mode of life of
various animals and the development of their instincts, becomes
our third source of evidence. I illustrated this in my first lecture
by discussing the growth of the slave-making instinct and of social
parasitism among ants.
Fourthly, we have the comparative embryology of our present
animals and plants. This subject is an important storehouse of
information in phylogenetic research, and it has made great progress
in recent times, for Oskar Hertwig's works have thrown much
light upon the embryology of the higher animals, and Korschelt
and Heider's upon that of invertebrates. Caution is necessary,
however, in making use of this source of evidence, as appears from
the history of the biogenetic fundamental law, laid down by Fritz
Miiller and Haeckel. According to this law, the ontogeny of the
individual is an abbreviated and somewhat modified repetition of
the phylogeny of the race ; but no such general law exists. Here
and there the ontogeny of an individual may give some hint that
is of importance in the investigation of its probable descent. In-
stances of this are the occurrence of teeth in the embryo of the
whalebone- whale, and the appearance of genuine wing-veins in the
imaginal development of the thoracic appendages in Termitoxenia.
THE DESCENT OF MAN 499
We come now to the question of the limits of evolution. Do facts
constrain us to believe evolution to be monophyletic or polyphyletic?
As I showed in my first lecture, there is no scientific proof of the
origin of the whole organic world from one primitive cell, nor of the
origin of the animal and vegetable kingdoms respectively from one
ancestral cell. On the contrary, facts point to a polyphyletic
evolution of both animals and plants, and not only palaeontology,
but also comparative morphology supports this view, as Boveri
has shown. What ideas ought we to have of this polyphyletic
evolution ? We cannot as yet even attempt to determine the number
of lines of descent in the animal and vegetable kingdoms, nor do we
know whence they proceed.
It is possible that in another hundred or thousand years we shall
know rather more about the phylogeny of living organisms than
we do now. All we can do is to continue our researches. In my
first lecture I referred to the idea of the natural or palseontological
species, which was originated by Neumayr and elaborated by
myself. Whoever bears in mind the above-mentioned limits of
evolution, which are imposed upon us by actual facts, will certainly
not go astray, Jle will not invent fanciful pedigrees a yard long,
which ultimately find favour only with social democrats under the
influence of monism, and not with the advocates of the scientific
theory of descent.
* # # * *
A series of photographs followed ; the first showed the transformation
of guests among Indian ants into termite-inquilines, thus illustrating the
formation of new species within comparatively recent times. This
picture afforded direct evidence for the theory of evolution, the others
supplied indirect evidence by illustrating the formation of new species,
genera, and families of beetles and flies in consequence of adaptation to
changed conditions of life in colonies of ants and termites.
Let us now pass on to something more important, Paulo majora
canamus !
We have seen that among plants and animals there is a good
deal of evidence in support of evolution, and this is based chiefly
upon palaeontology. It is more probable that the evolution was
polyphyletic, or in many lines of descent," than that it was
monophyletic; in fact, the former is the only really probable
hypothesis.
What are we to say regarding the descent of man, that all-
important question ? Are we to adopt the standpoint of natural
science, and say that man, like every other higher vertebrate, has
developed from the animal kingdom ?
I must not tmioh upon either the theological aspect of the
subject, or upon the abstract philosophical possibility of such an
evolution. I intend to deal with the matter from a practical point
of view only, and to discuss : (1) the spiritual evolution of man from
brutes ; (2) the bodily evolution.
2 K 2
500 INNSBKUCK LECTUKES
Let us see to what results science will lead us. In speaking
of purely natural evolution, I think we must reject the'theory that
man on his spiritual side can have been evolved from brutes, and
we need have no hesitation in doing so, as our rejection is justified
by modern experimental animal psychology. I am not discussing
monistic dogmas, nor the altogether unscientific popular practice
of ascribing to animals a spiritual life analogous to that of human
beings ; I am alluding only to the facts of animal psychology,
which, in its recent development, so far from bridging the old
chasm that Aristotelian philosophy has always recognised as
existing between the spiritual life of man and the sensitive life of
brutes, has widened it. I repeat : experimental animal psychology,
carried on in a critical spirit. Popular psychologists, such as
Biichner, Brehm, Marshall, Bolsche and others, are not, I think, to
be reckoned among the scientific representatives of animal psycho-
logy, the chief of whom are, in America, Thorndike, Kinnaman,
Hobhouse, Watson, &c. ; in Geneva, Claparede ; in Germany,
Wundt and Stumpf ; and in England, Lloyd Morgan. These are
unanimous in saying that we must not ascribe even to the higher
vertebrates any capacity for thought, or any power of abstraction
in the sense of ability to form rational concepts. The whole life
of an animal soul is limited to sense perception, imagination, and
instincts. What is called ' animal intelligence ' is nothing more
than the ability of an animal to learn by the experience of its senses.
It does not depend upon reflexion, but upon a repetition of definite
sense impressions, upon their combination in the creature's faculty
of sense imagination and their reproduction by sense memory.
Consequently an animal is taught by sense experience to change
its mode of action for its own advantage ; in other words, it is able
to learn. This is the conclusion at which modern animal psychology
has arrived, with reference to the spiritual difference between
man and brute. In my opinion it is confirmed by the psychology
of ants, and it does not justify us in abandoning the tenets of that
ancient philosophy which taught that the psychical endowment of
man and brute differed essentially. It is true that there is much
of the animal in man, but there is also something higher, viz. the
spiritual element in his being. I must not, however, dwell upon
this point now.
Let us turn to the aspect of the question with which natural
science can deal, and ask : 'What relation exists between man
and brutes with regard to their bodies ? Is the descent of man
from brute ancestors proved or not ? '
With regard to the formation of his body, his organs and systems
of organs, and the development of his nervous system, man stands
undoubtedly very close to the higher vertebrates. This fact cannot
be denied. But has natural science any one definite and well-
established theory to offer us on the subject of man's relationship
with the higher mammals ? On the contrary, there are a number
THE DESCENT OF MAN 501
of different hypotheses regarding the morphological descent of man.
Kohlbrugge has collected them in a thoroughly scientific article
and examined them, and the result is : Quot capita, tot sensus. We
have nothing to guide us but a set of mutually antagonistic hypo-
theses. This is the simple truth. When monists declare that the
descent of man from brutes is ' zoologically evident,' they have-
no more claim upon our consideration than Haeckel has, when
he calls the descent of man from apes ' an historical fact.'
The theories as to the relationship between man and brutes in
respect of their bodies may be divided roughly into two classes.
Some assume the existence of a direct relationship between man
and the higher apes, it is quite indifferent whether the forms in
question are still being or extinct. Others maintain the relationship
to be less close between man and apes, and seek the hypothetical
primitive form of man among mammals of a lower order. Both
classes of theories call for critical examination. The former numbers
among its supporters many of the more modern zoologists, the latter
finds more favour with anthropologists. The former is more
intelligible than the latter, which becomes hopelessly embarrassed
on the subject of the common ancestors of men and apes. Klaatsch,
who is one of the chief advocates of the second class of theories, at
a time when he had less clear opinions than he now possesses, used
to represent the common ancestor of man and ape as a * general
pithecoid type,' but he did not know where to place him. This
type proved to be much too general, and so Klaatsch has given
it up again in the last few years.
Stratz, another advocate of the theory of the distant relationship
between man and ape, imagined their common ancestor to be a
kind of Batrachian called a ' Molchmaus,' but most zoologists
are, like myself, still quite in the dark as to what kind of animal
that is. Morphologically, man resembles some of the lower orders
of mammals, such as the insect-eaters, more closely than the
anthropoid apes, but, nevertheless, the ' Molchmaus ' seems to me
scarcely suited to be a common ancestor of man and ape ; in fact,
a direct relationship between them would seem much more probable.
I should like at -this point to consider briefly the evidence in
support of both theories, but especially of that which regards man
as the direct descendant of the higher apes. Comparative mor-
phology supplies certain evidence, and it is undoubtedly true that
of all animals the higher apes bear most resemblance to man ;
there are in fact over a hundred points of resemblance ; but, on
the other hand, we must not overlook the great morphological
differences in the formation of the skeleton, of the cranium, &c., to
which attention was drawn long ago by Ranke, Virchow, Kollmann,
Bumiiller, and other anthropologists, who pointed out that in the
development of his extremities the ape .has outstript man, and that
man fits nowhere in the systematic succession of apes, neither at the
beginning nor anywhere else No one as yet has been able to
502 INNSBKUCK LECTURES
explain clearly the descent of man from an extinct form of ape.
Even Schwalbe's hypothesis on this subject has met with much
opposition from other specialists. I shall have to refer later to
the Pithecanthropus as a morphological connecting link. Selenka
thought that the great likeness between man and the anthropoid
apes in the formation of a placenta constituted a trustworthy
proof of direct relationship between them. Recently, however,
exactly the same placental formation has been shown to occur
in other animals, e.g. in a low kind of lemur (Tarsius spectrum)
found in Madagascar. It follows that this particular kind of
placental formation is due to adaptation to the needs of embryonic
existence, and, as a result of convergence, it may occur in creatures
that are not related. It is impossible to derive any argument in
favour of a direct relationship between man and the higher apes
from a likeness in their placental formation.
We come now to the evidence derived from comparative em-
bryology. What is known as the ' biogenetic fundamental law '
was enunciated by Fritz Miiller and elaborated by Haeckel. Accord-
ing to it, the ontogeny of an individual animal is an abbreviated
and partially modified repetition of its phylogeny, or the history
of its race. In its application to man this law found its dogmatic
expression in Haeckel's ' Progonotaxis hominis,' or genealogy of
man. It found its dogmatic expression, but nothing more, for, as
a matter of fact, precisely at this point there are so many exceptions
to the alleged general and fundamental law, that almost nothing is left
of it, the exception itself becomes the rule. I may mention, for
instance, the extraordinary development of the cerebral vesicles
in the human embryo ; it would certainly not be possible to find
any stage corresponding to them among our alleged ancestors, for any
creature possessing so huge a brain in comparison with its other
organs would have been a complete monstrosity. At the present
day scientific men in general are gradually becoming convinced
that it is impossible to claim for the biogenetic law that it is uni-
versally applicable. In support of this statement, I may refer
to very eminent authorities, such as Oppel, Keibel, and Oskar
Hertwig. Even Konrad Giinther does not venture to call it a law in
his work, ' Vom Urtier zum Menschen,' and he acts wisely, for the
biogenetic law, when it is logically applied, leads to consequences that
turn the doctrine of man's descent from apes simply upside down.
The law asserts that the ontogeny of the individual is an abbreviated
repetition of the evolution of the race. Now, in the ontogeny of the
higher apes there is a stage in the development of the cranium,
when the foetus very closely resembles a human being, but there
is not, in the case of the human embryo, a stage when, in its cranial
development, it resembles an ape. The logical conclusion from
this fact would be : Man is not descended from apes, but, on the
contrary, apes are descended from ancestors resembling men.
This deduction has actually been drawn by a number of eminent
THE DESCENT OF MAN 503
men, as Kohlbrugge pointed out. We used to hear a great deal
about the descent of man from fish, the theory being based upon
the fact that man in the course of his ontogeny is supposed to pass
through a fish-like stage. This theory, too, has been shattered by
Oskar Hertwig and other embryologists, who have proved that
the so-called branchial clefts and arches in the higher vertebrates
ought to be regarded as morphologically indifferent Anlg&ezL, whence
in the lower classes of vertebrates true gills are developed, whilst
in the higher classes they furnish material for quite different organs.
We have next to consider comparative blood-reactions, which
were believed to afford absolute proof of man'
with the anthropoid apes. A few years ago Friedenthal astonished
the world by proclaiming, as his discovery, that we were not only /
descended from apes, but were ourselves genuine apes. He based
this statement upon experiments made by himself, Uhlenhuth,
Nuttall, and others, on the reaction of different kinds of blood. Let
us see what is the real result of these experiments, and whether they
actually prove us to be blood-relations of apes, in the sense of
being their cousins. I have no hesitation in saying that they do
not prove it. The likeness between the higher apes and man in the
composition of their blood is indeed greater than the likeness between
the lower apes and man. I am quite ready to grant this, but there
are a number of questions belonging to physiological chemistry,
which throw fresh light upon the significance of these reactions.
Not long ago, at the last meeting of the Gorres Society at Ratisbon,
Dr. Baden, who is a specialist in physiological chemistry, read
a paper on experiments in blood-reaction and their bearing upon
the subject of phylogeny. The conclusion at which he arrived
was, that it was impossible to regard these experiments as affording
any actual proof of phylogenetic blood-relationship between man
and the higher apes ; we might just as well speak of a urine-relation-
ship between man and the higher vertebrates. All that these
experiments have proved is that in the composition of his blood —
blood being for zoologists only one of the tissues of the body — man
resembles the higher apes in many respects more than other animals.
It would be a great mistake to infer from this fact that man is
directly related in race to the anthropoid apes. Dr. Baden laid
particular stress upon the specific difference in the blood of men
and apes, and referred to recent works on this subject by Neisser,
Sachs, and others.
I was very glad that Friedenthal himself took part in the dis-
cussion that followed my Berlin lectures in 1907, and declared
that, in using the word ' blood-relationship,' he had never meant
anything more than a blood resemblance in the chemico-physiological
sense. It was a mistake on the part of writers on popular science to
say that by blood-relationship he understood actual kinship, and he
protested energetically against having such an idea imputed to him.
In speaking of blood-reactions, from the standpoint of organic
504 INNSBRUCK LECTUEES
chemistry, we are concerned only with the reactions of albumen,
with precipitins, haemolysins, &c. It has been observed that
the albumen in the lens of the eye shows the same composition in
very different kinds of vertebrates, but we cannot derive any
phylogenetic inference from this fact. It would be therefore
wrong and premature to infer that man is nothing but a genuine ape
from blood-reactions, which are likewise only reactions of albumen.
Finally, we have to speak of palaeontology, whence most of
the evidence in support of the theory of evolution is derived. What
does it tell us with regard to brute ancestors of man ? What
information does it give on the subject of the long-sought missing
link between man and apes ?
At the fifth International Congress of Zoologists at Berlin in 1901,
Professor Branco, one of our foremost palaeontologists, delivered
a very outspoken address on the subject of fossil man, and his
conclusion was that hitherto palaeontology has no knowledge at all
of any ancestors of man. This was certainly a very honest statement,
made by an eminent scholar. Let us now consider more closely
the facts bearing upon the subject. For some time it was believed
that the missing link between man and the higher apes had been
discovered in the so-called Pithecanthropus erectus, the ape-man,
whose remains were found in Java in 1 89 1 . At the third International
Congress of Zoologists, held at Leyden in 1895, Eugene Dubois read
a very interesting paper about them ; the remains found consisted
of a cranium, a femur, and first one and then a second molar tooth.
Dubois spoke for a couple of hours, trying to construct from these
remains a connecting link between ape and man, that was neither
an ape nor a man, but an ape-man, standing between the two.
Privy-Councillor Virchow was presiding over the meeting, and
listened to all that Dubois said with the impenetrable expression of
a diplomatist. I wondered what attitude he would assume towards
the question. At the conclusion of the lecture Virchow began by
thanking Dubois for his kind invitation to be present, and did not
allude to the fact that the discovered remains had been shown him
only just before the meeting, although he had telegraphed three
times, asking to see them. He spoke highly of the lecturer's acumen,
but said that in his own opinion it was impossible to decide whether
the fragments had formed part of one individual, and still more
impossible to ascertain whether they belonged to a human being or
an ape. This point could not, he said, be settled until we possessed
a complete skeleton. Virchow then pronounced the cranium to be
that of a large ape, but he thought the femur and the teeth were
probably human. Such was Virchow's opinion on that occasion.
Has it been modified subsequently ? Further examination of this
famous Pithecanthropus has led most scientific men to regard him
as a genuine ape belonging to the group of Hylobatidae ; others,
however, consider him at best to be an ideal, but not a real
intermediate form between man and ape. I say ' at best an ideal
intermediate form,' inasmuch as certain peculiarities in the formation
THE DESCENT OF MAN 505
of his cranium and skeleton cause him to approximate more closely to
man than do any of the present anthropoid apes. But, on the
other hand, there are other morphological peculiarities which suggest
his being more nearly connected with the lower apes. Schwalbe has
drawn attention to these points, and for these reasons the scientific
opinion, which seems most likely to be correct, is that of the zoologists
who regard the Pithecanthropus as one of the higher apes, representing
the end of one side branch of the line of apes. In the case of
Pithecanthropus we have a repetition of the old comedy ; a supposed
link in the ancestry of man is at first welcomed with enthusiasm,
but finally has to be discarded.
In a subsequent photograph I shall show you how the zoologists
assembled at Leyden in 1895 allowed the Pithecanthropus to be
presented to them as a * masher,' to enliven them at their banquet.
Here arises the important question of the age of the Pithecan-
thropus.
At first he was believed to have lived in the Tertiary period. As
human remains cannot with certainty be assigned to any epoch
before the middle Pleistocene — it is at least doubtful whether the
Heidelberg lower jaw is really early Pleistocene — we can easily
understand why in 1895 it was still possible to seek an ancestor of
the human race in the ape-man. More recent investigations made
in Java by Voltz and Elbert have transferred the ape-man into
the Pleistocene epoch, and, as Branco stated in 1908, he probably
lived about the middle of it, and hence he could not have been
an ancestor of man, as he was a contemporary of man at that time.
Homo primigenius has played a much more important part than
the Pithecanthropus, and soon replaced him in the theories of those
advocates of evolution who felt it absolutely necessary to discover
an intermediate form. This primitive man is in reality the oldest
palaeolithic man of whom we know anything, and in him science has
found true, positive points d'appui.
# # * * *
In 1901 Schwalbe submitted the Neandertal cranium to a fresh
examination, in consequence of which he added a twelfth to the
already existing eleven theories about it. In the Banner Jahr-
bftcher he put forward the hypothesis that the Neandertal man was
not a man at all, but the representative of a distinct genus, that ought
to be placed systematically between Pithecanthropus and fossil man.
The Neandertal cranium was found in a cave in the Diissel Valley
near the Rhine about the middle of last century. At the time
Virchow considered it to be a pathological formation. He thought
that people with similar crania were still to be met with. His
opinion was mistaken in one way, but quite correct in another.
Modern research has shown that the Neandertal type does not occur
amongst Europeans of the present day, although it may be found
amongst Australian blacks. As a fossil or primitive man, the Nean-
dertal type represents that of early palaeolithic man, who cannot be
relegated to a time further back than the middle of the Pleistocene
506 INNSBKUCK LECTUKES
epoch. Obermaier assigns his first appearance to the last third
of that epoch, viz. to the last interglacial or Mousterian. To
the same date must be assigned the remains found in the South of
France, to which I shall refer later, and which archseologically admit
of very precise verification.
This does not agree with Schwalbe's view, expressed in 1901, that
the Neandertal man was a representative of a distinct genus standing
midway between man and the Pithecanthropus, Schwalbe himself
changed his mind on the subject in 1904, at the meeting of the
Association of German Naturalists and Physicians, when he spoke
of Homo primigenius as a distinct species of man, not as a genus.
Schwalbe believed him to be distinguished both from modern and
from later palaeolithic man by a number of constant characteristics,
of which the chief are a receding forehead, a lower cranium, pro-
minent ridges above the eyes and absence of chin, or rather of the
furrow in the lower jaw, which gives rise to the projecting chin
common at the present day.
But this opinion also, that Homo primigenius represents a
particular species, is now untenable, and has been abandoned by
almost all scientific men, even by its author, Professor Schwalbe.
The first blow was dealt it by the discoveries made at Krapina in
Croatia. In 1905 Gorganovic Kramberger, who found the remains
there, showed that it was possible to trace a series of gradual transi-
tions between Homo primigenius and modern man, and consequently,
according to the principles of zoological classification, primitive
man cannot be regarded as a different species, but only as an older
race of man, who made his appearance in the middle of the Pleisto-
cene epoch. There is most convincing evidence in support of this
latter theory, in fact, if we accept Obermaier's redistribution of
the glacial epochs, we must assign the appearance of man to the
last third of the Pleistocene. No one at the present day can doubt
that Homo primigenius represents a distinct, early palaeolithic race
of men, for this has been conclusively proved by paleontology.
We have remains from the Diissel Valley near the Rhine, from
Spy and Nalautte in Belgium, from Ochoz in Moravia, from Kra*pina
in Croatia, and from le Moustier and Chapelle-aux-Saints in the
south of France, and much has been learnt from them. An impor-
tant discovery has been made lately in Germany, for at Mauer, near
Heidelberg, Schoetensack found a human jaw-bone, which, in his
opinion, either is late Tertiary, or belongs to the close of the Tertiary
and the beginning of the Quaternary periods. Obermaier and Wilser,
however, rightly questioned the accuracy of this date, and showed
that the bones found with the jaw were those of animals which
might with equal probability be assigned to the Pleistocene epoch.
There is very little difference in size and shape between the jaw-
bones found at Mauer and Spy respectively ; the latter undoubtedly
belongs to the Neandertal type. The massive development of the
lower jaw in comparison with the smallness of the teeth is certainly
remarkable, but exactly the same features occur in a modern
THE DESCENT OF MAN 507
Eskimo skull, shown me a few days ago by Birkner, in the collection
of the Munich Institute for Palaeontology. The Mauer jaw belongs
morphologically to the Neandertal type,1 and, as I have just said,
it is probably not early, but middle Pleistocene.
Owing to the absence of palaeolithic stone implements in the
Heidelberg deposits, we are certainly not justified in assigning the
jaw-bone to any definite period, such as the Chellean or Mousterian.
But for this reason to assert, as Schoetensack did, that the owner
of the bone was a Tertiary man, and perhaps even a common ancestor
of man and anthropoid apes, is too daring a statement, and by no
means well established. We can do nothing but wait and see
what future research will reveal.
All that we know for certain on this subject at the present
time is that an early race of men lived in Central Europe in the latter
part of the Pleistocene epoch, and that they were distinguished from
the modern inhabitants of Europe by definite, although slight,
anatomical and morphological characteristics, such as the strong
development of ridges above the eyes, low forehead, receding chin,
&c. But, as Klaatsch has proved convincingly, all these peculiar-
ities still occur in Australian blacks. Therefore primitive man, in
respect of his body, only belonged to an earlier race of man, and
was not a half-ape.
Let us consider the chief of these characteristics somewhat
more closely, in order to see whether they really are points of likeness
to apes or not. The receding chin is due to a stronger, but quite
normal development of the lower jaw. It was only when the lower
jaw began to degenerate that the hollow was formed, which causes
the chin to project. I cannot now discuss the little bones of the
chin, which are morphologically connected with this projection,
but the diminution in size of the lower jaw, and the pretty dimple
that we now admire, are, considered in their morphological aspect,
marks not of progressive but of retrograde development in the
formation of the lower jaw. As men became more civilised and
adopted a more refined sort of food, their jaws had less hard work
to perform than those of primitive men, and consequently dimin-
ished in size. With regard to the prominent ridges above the eyes,
—the second great peculiarity of the earliest race of men — Klaatsch
explained last year, at the meeting of naturalists in Cologne, that
they were connected with the size of the eye-sockets, and therefore
with the adaptation of early palaeolithic man to the life of a hunter.
They are a function of the very marked development of his sense
of sight, and there is nothing pithecoid about them.
1 Kramberger has recently shown that in its solid formation the Heidel-
berg jawbone very closely resembles that of a modern Eskimo skull, the chief
difference between them being that the chin is more pronounced in the latter
than in the former. This confirms the conclusion that the Heidelberg jaw
belonged to a man of the Neandertal type. See « Der Unterkiefer der Eskimo,
als Trager primitiver Merkmale ' (Sitzungslericht der Preuss. Akad. der
Wissenschaften, 1909).
508 INNSBKUCK LECTURES
Some one apparently dreamed (and his dream has been spread
far and wide in French newspapers) that primitive man could not
walk upright, but advanced, like apes, in a crouching attitude.
Klaatsch has publicly called this idea ' nonsense.'
The extremities of the le Moustier man may, by their remarkable
shortness, suggest adaptation to cave life, but they are not pithecoid,
for apes have much longer arms than we have.
We must investigate the cranial development in palaeolithic
man somewhat more closely. Did the earliest man known to us
stand, with respect to his cranial capacity, somewhere midway
between apes and modern men ? Certainly not. The cranial
capacity of no anthropoid ape reaches 650 cubic centimetres ; 1
in the fossil Pithecanthropus, a gigantic ape, it amounts to 800-850 c.c.
The Weddas, a race of dwarfs in Ceylon, have the smallest cranial
capacity among human beings ; in their case it is about 960 c.c.
In making this statement we are, of course, comparing the absolute
measurement of the head of a giant ape with that of a human
dwarf. The Neandertal cranium was said to have a capacity of
about 1230 c.c., whilst now men in Central Europe (Bavaria) possess
on an average a cranial capacity of about 1503 c.c. The capacity
of a female cranium is about 200 c.c. less than that of a male, but
this does not prove women to be less intelligent than men. Bis-
marck's skull was enormous, and had a capacity of 1965 c.c., but
Virchow discovered one still larger, with a capacity of 2010 c.c.,
and this skull belonged to a savage in New Britain, not to a civilised
inhabitant of Great Britain. This is the largest skull on record.
Where does primitive man stand in comparison ? Boule has
recently made a very careful examination of the remarkable human
remains found at Chapelle-aux-Saints, and, as the cranium was
in very good preservation, he was able to test its capacity according
to the newest methods, and what was the result ? Did he find
that it measured about 1230 c.c., the number formerly assumed to
be that of the Neandertal type ? This would correspond very
closely with the cranial capacity of women at the present day.
No, the skulls of these oldest palaeolithic men vary in respect of their
capacity from 1600 to 1700 c.c.; probably 1626 or 1635 c.c. is a safe
average to take.
According to the materialistic school, the capacity of the skull
affords a direct indication of the mental capabilities of its owner ;
and if this be so, we are justified in asking what has become of
the half-ape ? Among human beings of our own time only a few
have a cranial capacity greater than that of this fortunate half-ape,
not even our most learned university professors, who are rightly
considered the elite of the human race in respect of intellect.
There seems to be need of greater moderation and caution in
1 Ranke gives 605 c.c. as the maximum for the male gorilla ; Topinard
thinks the number may reach 621.
THE DESCENT OF MAN 509
accepting the theory that man is the descendant of brutes. We
must consult facts, and proceed quietly without reference to the
dogmas of monism. I can give an instance of what I mean by
consulting facts, connected with the skull from le Moustier. I
had opportunity to examine it closely at a lecture given by Hauser
to the Anthropological Association at Frankfurt-am-Main in 1908.
Klaatsch's reconstruction of it was noticeably different from
the plaster model that stood beside it ; 1 the latter bore a strong
resemblance, absent in the original, to an ape, especially about the
mouth, and this was due to the fact that, through a blunder in
taking the cast, in the plaster model the ends of the lower jaw were
at a distance of several centimetres from their sockets. In reality,
the same relative proportion between the size of the cranium and
that of the lower part of the face exists in the le Moustier skull as
in Homo sapiens recens. You will see this clearly in the photo-
graphs of this skull which are copies of those made originally by
Hauser and Klaatsch.
May we say then that these palseontological discoveries have
given a scientific account of the origin of man ? No, we are still far
from it. We know that the geologically oldest human beings
hitherto known, belonging to the Stone Age of Central Europe,
formed a race known as the Neandertal race, but this by no means
represents a connecting link between apes and men. We know
further that critical investigations made by Boule, Obermaier, and
de Lapparent have completely overthrown the belief, based upon
Rutot's once famous Eolithic Theory, that even at the beginning
of the Tertiary ^period there existed beings resembling men, who
fashioned rough flint implements. De Lapparent not unfairly
calls the eoliths ' silex tailles par eux-memes,' because they may
have been formed by the mere forces of nature. But we do not
know if the Neandertal man was really the earliest man, for we
cannot tell whence he came. Did he appear as an autochthon in
central Europe ? Did he migrate hither from the east ? As
a migration from the east or south can be proved in the case of
almost all subsequent European races, it very probably occurred
also in the case of Homo primigenius, who bears the proud name
of first-born among the human race. The negro-like Grimaldi-type
of South European, which appears at the close of the Pleistocene
epoch, most likely came from the south. In the parts of southern
France where remains of the Neandertal type of early palaeolithic
man are discovered, viz. in the valleys of the Dordogne and of
the Vezere, in somewhat higher strata are found traces of a later
palaeolithic man of the Cro-Magnon type. He belongs to the
close of the Pleistocene epoch, and in his cranial formation he is
exactly like Central Europeans of the present time. Was he a
1 Cf. the accompanying illustration, which is a copy of Hauser's original
photograph.
510 INNSBKUCK LECTUEES
descendant of the primitive man, who inhabited the same regions
before him ? Or did he migrate hither from the east, from western
or central Asia ? We do not know ; nor do we know whether
the Neandertal type of man who differed from the latter type in
some rough morphological characteristics, was himself a descendant
of another, still older race, that migrated from the east about
the middle of the Pleistocene epoch.
We have no certain information as to the outward appearance
of the oldest man. We cannot tell whether he was like the earliest
palaeolithic European, or whether he belonged to a higher race, more
like modern men, and only acquired the bodily peculiarities of
the Neandertal type by adaptation to the life of a cave-dweller and
hunter.
| The history of the human race is still silent with regard to these
Joints ; but we are sure of one thing, that the oldest palaeolithic
Iaan of whom we have any knowledge, even if he had not attained
to a high degree of civilisation, possessed the capacity for being
/civilised. He discovered the use of fire, and found out how to
/make the most important implements which we still employ,
I such as the knife, the axe, and the scraper. In the flint implements
I of this period we can trace the simplest ideas underlying the con-
I struction of our most indispensable tools. He must indeed have
I been a clever man !
Picture to yourselves a modern civilised human being, bereft
of all the means of existence, and devoid of all knowledge how to
make tools ; I assure you, the poor fellow would probably starve.
And yet our ancestor, who is represented as being something between
ape and man, succeeded in making his way through the world !
He deserves honour, and ought not to be contemptuously spoken of
as a half-ape !
I must unfortunately cut short this part of my lecture . . .
and will therefore pass on at once to the photographs that I have
to show you. They bear upon the comparative morphology of
man and ape, and upon primitive man.
The first two photographs represented skeletons of an orang-utang
and of a man respectively (from the Army and Navy Medical Museum in
Washington) ; they illustrated the differences between man and ape in
the formation of the extremities, the excessive length of the ape's arm
and the peculiarity of its foot.
The next two photographs represented the crania of the orang-utang
and of a man respectively. In the ape's skull, the skull-cap is very small
in comparison with the enormously developed lower part of the face with
its powerful jaws. The brain region is insignificant in comparison with
the parts concerned in devouring food. In man the case is reversed. The
lower part of the face is very small in comparison with the large skull-cap,
which contains the brain.
The fifth photograph showed the Pithecanthropus as a * masher,' as
he appeared at the banquet given to the Zoologists assembled at Leyden
in 1895.
THE DESCENT OF MAN 511
The sixth photograph represented the Neandertal cranium, according
to Schaafhausen's illustration of it.
The seventh showed the cranial curves of a chimpanzee, the Pithecan-
thropus, the Neandertal man, a modern Australian black, and a modern
Englishman, according to Macnamara. The crania of the ape and of the
Pithecanthropus were seen to differ only in size ; those of the Neandertal
man and of the Australian black resembled one another so closely as both
to be within the limits of variation of Homo sapiens.
The eighth and ninth photographs were copies from originals, taken by
Hauser and Klaatsch, of the skull of the le Moustier man. The size of the
cranium, in comparison with the lower part of the face, is relatively almost
the same as in modern men, although both are absolutely larger than is
the case in most modern skulls. After the lecturer had pointed out on
these photographs the characteristics of the Neandertal type, he described
the circumstances under which the le Moustier skeleton was discovered.
In its case, as in that of the skeleton at Chapelle-aux-Saints, there were
unmistakable tokens of solemn burial in the early paleolithic age. The
body was laid on its side, the arms and legs being arranged in a definite
position. Under the head was a cushion of earth, upon which, at le
Moustier, the impression of the dead man's cheek could still be seen. The
lecturer said that he had examined the remains found by Hauser. and con-
vinced himself of the truth of this statement. Round about the corpse
were arranged the largest and finest stone implements of the period, as
Hauser had carefully pointed out. The le Moustier skeleton was that
of a young man, whose parents had buried with their child all the precious
things that they possessed. Can they have been ' bestial savages,' or
- fierce ape-men ' ? In a lecture delivered at Cologne in 1908 at the
meeting of German Naturalists and Physicians, Klaatsch remarked that
the mode of burial of this Homo mousteriensis pointed quite plainly to
belief in immortality existing in the mind of palaeolithic primitive man
perhaps 30,000 years ago.1
As far as the time at my disposal permitted, I have laid before
you what science teaches us regarding our ancestry. And what
does it amount to ? We arrive at exactly the same result as Branco
did eight years ago, when he stated, at the International Congress
of Zoologists at Berlin, that palaeontology at the present time
knows no ancestors of man. This statement has been confirmed by
recent research into the primitive history of the human race.
We are acquainted with an early palaeolithic race, called the
Neandertal type or Homo primigenius, but we are not acquainted
with any ancestors of man resembling apes. The most remote
ancestor of man hitherto discovered by science was both in body
and mind a genuine human being, a true Homo sapiens.
If this be true, what scientific justification is there for Haeckel's
1 In speaking of time we are at present unable to do more than offer specu-
lations. We have to estimate the length of periods by changes in the fauna
and flora, which again are a result of modifications in climate. The latter,
however, especially the alternation of glacial and interglacial periods, are
probably connected with the nutation of the earth's axis. For this reason
we must assume that the last interglacial period, to which the Mousterian
deposits belong, occurred at least 30,000 years ago (Obermaier).
512 INNSBRUCK LECTUEES
' Pedigree of the Primates,' in which, even in 1907, Homo stupidus,
the stupid man, appears as the immediate predecessor of Homo
sapiens ? There is no scientific justification at all for it. For
the last forty years, Haeckel has been devising such pedigrees of
man, and has been proclaiming to the whole world the descent of
man from apes — for his Primates are the half-apes and the true apes
— as an historical fact, but this cannot be called pursuit of science,
but rather mischievous meddling with it.
On February 18, 1907, at the evening discussion that followed
my Berlin lectures, Haeckel's assistant, Dr. Schmidt of Jena,
came forward and solemnly defended his master against the charge,
that I had brought against him, of having published his ' Pedigree of
the Primates ' as an historical fact. He maintained that Haeckel
had never done so, being far too modest and far too ardent a lover
of truth ; but in my concluding speech there was no need for me to
do more than quote one passage from Haeckel's work, ' The Last
Link : Our Present Knowledge of the Descent of Man,' in which no
one can deny that ' the phyletic unity of the line of primates from
the lemurs (or half-apes) to man ' is declared to be an ' historical
fact.' With such a passage before him, no one could assert that
Haeckel never said anything of the sort. Nevertheless, on the
following morning, a few daily papers, not, it is true, of the highest
class, accused me of having falsified the quotation. This may be
called pursuit of science on the lines of monism and social democracy,
but it cannot be described as a justification of Haeckel's pedigrees of
man.
But Haeckel may possibly have improved lately ? Yes, a little,
but not much. In honour of the opening of the new Phyletic
Museum at Jena in 1908, Haeckel published a large folio bearing
the magnificent title ' Progono taxis hominis.' In this work
he has at last corrected some of the false statements to which
he had clung so tenaciously. The unfortunate Homo stupidus
has now vanished from the pedigree of man, and his place is
taken by Homo primigenius. It was indeed high time, for the
latter was discovered fifty years ago ! Haeckel remarks too that
many geologists consider the Pithecanthropus from Java to belong
to the Pleistocene and not to the Tertiary period. He ought
to have said simply ' geologists,' but nevertheless these words show
an advance upon his previous assertions. The advance is, however,
only in the text; when we turn to the pedigree of primates, which
is given in the appendix, we find that there he has gone backwards
rather than forwards. Beside the name Pithecanthropus erectus
stands, as before, the word ' Pliocene,' i.e. late Tertiary, and Homo
primigenius is represented as the descendant of this ape-man,
although the latter was really a contemporary of man of the Pleisto-
cene epoch. Such is Haeckel's ' scientific spirit ! ' Elsewhere, too,
this scientific work contains manifest contradictions. In the text
all the early races of men are changed into so many species, but on
HAECKEL ON THE DESCENT OF MAN 513
the pedigree of primates they appear again as races, and not as
species. How are such blunders possible in a scientific publication
of this sort ? The only true explanation was suggested to me in
Munich a few days ago by an eminent zoologist, who had been a
pupil of Haeckel's. He ascribed them to senile decay ! But even
this explanation breaks down, when we find, on the most recent
pedigree, that Haeckel has set the same mark against the ancestors
that he has invented in the pedigree of man, as against the fossil
forms of extinct primates. The same little cross stands beside
both, as a sign that both are extinct. A scientific man really is
going too far when he sets purely imaginary forms on a level with
real fossils, in order to deceive his reader as to the true value of
this human pedigree ; to say the least of it, he is playing tricks and
juggling with the truth, or, to use plainer language, he is telling lies !
I come now to the charge, which Brass, has recently brought
against Haeckel. of having tampered with the illustrations of
embryos.i This charge has attracted much attention, at which I
am surprised, for, in the first place, the alleged falsifications of illus-
trations are by no means the worst falsifications perpetrated by
Haeckel. It is far worse that for more than forty years he has been
falsifying men's ideas, and so has robbed the German nation of
Christianity, and given it instead a materialistic and atheistic
cosmogony. To distort the Christian conception of God and I
represent Him" as a ' gaseous vertebrate ' is a far worse fraud on
Haeckel's part than tampering with a thousand pictures of embryos.
In the second place, the charge, brought by Brass against Haeckel, of
having tampered with the illustrations, was by no means new.2
The same accusation was raised against Haeckel by Kiitimeyer, a
Swiss zoologist, as early as 1868, and by Anton His of Leipzig, a
famous anatomist, in 1874, and was then proved to be irrefutable.
It is really an ' historical fact ' that Haeckel, for the sake of his
argument, i.e. in order to convince his readers thoroughly of their
descent from brutes, caused the same plate to be printed three times
in his ' History of Creation,' and said that it represented three
distinct objects extremely like one another. Haeckel himself sub-
sequently acknowledged that he had done so. It is another ' his-
torical fact ' that in his ' Anthropogeny ' he altered many illustra-
tions of embryos in an arbitrary manner, and assigned to them other
names than those which they had originally borne, and thereby he
caused His and other colleagues publicly to declare that Haeckel was
not seriously carrying on scientific research. In replying to this
charge in 1891, Haeckel defended himself in a classical fashion by
calling His, Kolliker, and other eminent German embryologists ' a
1 This subject is treated more fully here than it was in the lecture, when
want of time compelled me to be very brief.
2 On this subject see my article in Stimmen aus Maria-Laach for 1909,
Nos. 2-4, ' Alte und neue Forschungen Haeckels iiber das Menschenproblem.'
2 L
514 INNSBKUCK LECTUEES
company of Scribes and Pharisees,' who ought to be described as
' narrow-minded ' rather than as ' exact scientists.'
I come now to the famous declaration of forty-six German
zoologists on the subject of the dispute between Haeckel and Brass.
In all probability this declaration attracted so much attention
chiefly because people assumed it to be an ' amende honorable ' to
Haeckel. Perhaps a consideration of its origin will lead them to
form another opinion. In his reply to Brass, Haeckel boldly asserted
that if he were to be accused of falsifying the illustrations of em-
bryos, a similar accusation must be brought against hundreds of
highly respected embryologists, anatomists, zoologists, &c., for
they had had recourse to falsification as much as he himself, and
had in many ways ' schematised ' their illustrations. This was
certainly too daring a suggestion on Haeckel's part. He knew well
enough that other scientific men do not ' schematise ' in his fashion,
for they say what they have done, if they present us with an imagin-
ary form, or alter an existing form to reproduce it in a schematic
fashion. Frank acknowledgments of this kind are missing in
Haeckel's falsified illustrations of embryos, and so by means of
them he has deceived his readers as to the worth or rather the
worthlessness of the evidence that they afford of the descent of man
from brutes. It was therefore absolutely necessary for Haeckel's
German colleagues to adopt some definite attitude in answer to
Haeckel's suggestion that they all were guilty of falsification as
much as he was. The famous declaration was their reply to this
insinuation.
It is obvious that the successors of those exact German scientists,
who denounced Haeckel's proceedings so decidedly thirty years ago,
and were in consequence called by him ' narrow-minded,' could not in
their declaration express approval of Haeckel's action on the point
on which Brass challenged him, but only disapproval. This they
did in unmistakable terms, but they were afraid of injuring, not
only Haeckel's reputation, but also that of the whole scientific
doctrine of evolution. For this reason they ostensibly directed
their censure chiefly against the ' Keplerbund.' This was a clumsy
device on their part, for the ' Keplerbund ' is no more opposed to
the scientific doctrine of evolution than I am. Moreover, there was
no ground for their fear lest a declaration against Haeckel should
damage the reputation of science, for no one during the last forty
years has done more than Haeckel to compromise the scientific
doctrine of evolution in Germany, since he has boldly misused it in
his attack upon Christianity. For some reason or other, however,
the forty-six zoologists insisted upon the insertion of the clause
against the ' Keplerbund ' in their declaration against Haeckel,
but I do not think that thereby its significance is diminished, in
so far as it refers to Haeckel's proceedings.
I am confirmed in this view by the circumstances under which
the declaration was issued. It was signed by a very considerable
MONISM 515
number of German zoologists, some of whom I know personally as
men of calm judgment, highly esteemed in the scientific world. In
the Deutsche Medizinische Wochenschrift for 1909 — I think in the
eighth number — an article on the dispute between Haeckel and
Brass had appeared, written by Professor Keibel of Freiburg i. B.,
one of our most respected German authorities on the subject of
the comparative embryology of man and the higher animals. In this
article Keibel criticized HaeckePs illustrations of embryos very
sharply, and completely confirmed the disclosures made by Brass
regarding Haeckel's so-called ' falsifications.' It is true that
Keibel did not speak of falsifications but of inaccuracies. The word,
however, is a matter of choice ; personally, I believe inaccuracies
originating in an intention to mislead the reader . are not mere
inaccuracies. For instance, when Haeckel alters an illustration
of the embryo of an ape with a tail, so as to turn it into the picture
of one without a tail, and at the same time changes the name of the
creature, it can hardly be done unintentionally.
We are not here concerned with Keibel's further statements
against Brass in the article to which I have referred. It is true
that Brass's work is not free from inaccuracies, but it certainly
is free from any intention to deceive the reader.
The declaration of the forty-six zoologists followed Professor
Keibel's absolutely crushing criticism of Haeckel in the Deutsche
Medizinische Wochenschrift, and, in my opinion, in signing the
former they expressed their agreement with the latter. In this way
the declaration of the forty-six acquires another significance than
that hitherto ascribed to it. I regard it as an exculpation, not of
Haeckel, but of German science !
I may call attention to the further fact that among the publica-
tions of the * Keplerbund ' there has recently appeared a pamphlet
written by Director Teudt, in a very calm and impartial spirit,
entitled * Im Interesse der Wissenschaft ' (In the Interests of Science).
It contains an account of the dispute between Haeckel and Brass,
and of the publications dealing with it. It does not, however,
connect the declaration of the forty-six zoologists with Keibel's
criticism of Haeckel. As the declaration appeared almost simul-
taneously in a great number of magazines and newspapers, it is
quite possible that this connexion, which is certainly to the
advantage of the forty-six, has been too much overlooked.
Before leaving this subject, let me say a few serious words on
the claim made by monism of having replaced the Christian cos-
mogony by a new and better theory of the universe. This new
monistic doctrine is being actively propagated at the present time,
both in academic circles and among the lower classes. It behoves us
to ask what monism really is.
The word ' monism ' is a genuine Proteus ; for all kinds of various
meanings are concealed under it, and it is absolutely necessary for
us to arrive at some clear conception of what it is, in order to be
2 L 2
516 INNSBKUCK LECTUEES
able to combat the mischief that is being done with this catch-word
' monism.'
Literally translated it means * Doctrine of Unity.' This suggests
the pantheistic principle of the One ; but we cannot at once adopt
this as our definition. In the course of his speech at the evening
discussion in Berlin on February 18, 1907, Professor Plate declared
that the monist concerned himself only with natural laws, not
with what lay behind them, with regard to which different men
held different opinions. This would lead us to suppose monism
to be synonymous with agnosticism, which denies that God can be
known and rejects all metaphysics. But here we have a confusion
of ideas rather than a definition. Agnosticism is not synonymous
with monism, at least for any one who has had any philosophical
training. The essence of monism possibly is, that some of the
people who call themselves monists think of the unknown quantity
x underlying the natural laws in one way, and others in another.
This, however, would not be monism in the philosophical sense
of the word, and would be more suitably designated ' confusionism.'
What is the real meaning of monism of which we hear so much
nowadays ?
Plate, having probably forgotten the definition that he had
previously given, offered another in the book written against me :
' Ultramontane Weltanschauung und moderne Lebenskunde,
Orthodoxie und Monismus ' (Ultramontane cosmogony and modern
views of life; Orthodoxy and Monism). The defective objectivity
of this work reveals itself even in its title. It is a faithful reflexion
of the line of action — equally wanting in objectivity and equally
unsuccessful — adopted by Plate and some others of my opponents at
the evening discussion in Berlin, on February 18, 1907. A very
sarcastic and shrewd criticism of their proceedings appeared in
the Munich Hochschulnachrichten (1908, No. 6), which certainly
cannot be suspected of clericalism. The writer remarked that they
had not treated their guest with any particular consideration, but
nevertheless they had not succeeded in positively refuting his
statements ; annoyed at the appearance of a Jesuit, these worthy
Berlin gentlemen had dragged into the discussion questions that had
nothing to do with it, and this deserved notice as a characteristic
feature of the times ! — Plate and his companions were ill-advised
when they attempted to use a discussion of the scientific theory of
evolution as an opportunity for attacking the Catholic Church.
In the work to which I am referring, Plate solemnly declares that
every student of nature must necessarily be a monist ; if he is
not, he must be wanting either in ability to reason or in honest love
of truth. But what does Plate mean by ' monism ' in this passage ?
Something quite different from what he meant before. In this
place monism is an effort to obtain as uniform and simple a theory
of the universe as possible in accordance with natural science.
If this is monism, Plate is perfectly right in declaring every
i
MONISM 517
student of nature, who does not call himself a monist, to be either
a fool or a hypocrite. In this sense, as aiming at a very uniform
and simple explanation of nature, I too am a monist ; Father Secchi
was a monist when he wrote his ' L'unita delle forze fisiche,' and
even St. Thomas Aquinas, Blessed Albert the Great, and St. Augus-
tine were downright monists, for all earnest thinkers in every age,
as soon as they have begun to study nature, have striven to
find the most uniform and simple explanation possible fox its
phenomena.
What can we say of this definition of monism given by Plate,
a member of the German ' Monistenbund,' of which Haeckel is
president ?
We can only say that it is calculated to mislead the general
public, just after HaeckePs fashion ; monism is first defined in such
a way that every thoughtful student of nature must be a monist,
and then we are told : ' Wasmann and Keinke^ and all adherents of
Christianity are opposed TxTmonism, therefore they are either fools
or hypocrites.' About such an argument as this it is not possible
to say anything but that it is absolutely dishonest.
You are right in thinking that behind monism, as repre-
sented by Plate and the ' Monistenbund,' there lurks something
quite different from a desire for a uniform explanation of natural
phenomena. It is a name for a number of dogmatic hypotheses,
which have nothing at all to do with a scientific account of natural
phenomena.
One of these hypotheses is especially connected with the theory
of evolution ; Plate, Forel, Escherich, Wagner, and other monists
maintain that ' scientifically ' only a monistic theory of evolution is
admissible, i.e. a theory of descent, according to which the whole
evolution of the organic world, or at least of the two organic king-
doms, must form one single line, in which the higher forms have
proceeded from the lower, and these again from one or a few primi-
tive cells. These representatives of monism ridicule the idea of a
polyphyletic evolution of animals and plants, and try to cast upon
it a suspicion of being ' theological,' as several of my monistic
opponents have done. They are intolerant of my conception of
' natural species,' which groups together as forming a natural unit
all the species, genera, and families belonging to one palseontological
line of descent. Therefore they maintain the conception of natural
species to be theological, and consistent with neither natural science
nor natural philosophy. Apparently these gentlemen are not
aware that many years ago Neumayr stated his ideas regarding
' palseontological species,' which exactly coincide with my own
regarding ' natural species,' and yet Neumayr was neither a theo-
logian nor a Jesuit. Here we have another instance of the monists'
vaunted freedom from prejudice ! They begin by asserting that
only a monistic, monophyletic evolution can have any scientific
justification, and they entirely forget that the question of the limits
518 INNSBRUCK LECTUBES
of race- evolution is one of facts and not of dogmas. In the first of
my lectures I discussed this point more fully.
Another dogmatic presupposition on the part of monism, as
represented by Haeckel and the German ' Monistenbund,' is con-
tained in the assertion that it is indispensable to the unity and
simplicity of any explanation of natural phenomena, that the whole
natural world should have been evolved in conformity with one
and the same law. Behind this assertion lurks the further assump-
tion that this universal law must be purely mechanical. Of course,
every monist is at liberty to ascribe to each atom in the universe the
possession of a ' soul,' which, however, consists merely of an
attracting and repelling force ; although, as Dubois-Reymond
shrewdly remarks, to do so is an insult to all reasonable philosophic
thought.
From the scientific point of view, what are we to think of the
claims of monism ?
In the first place, monism is absolute dogmatism, and appeals
in vain to its ' scientific character.' It is an absolutely dogmatic
/ assumption to declare that one and tEe same law must necessarily
govern the evolution of the inanimate and of the animate world of
plants and of animals. No less dogmatic is the further assumption
that this sole law governing evolution must have been, and must
still be, purely mechanical.
Theories in natural philosophy must be based upon actual
scientific results ; it is only thus that they can have any scientific
foundation. Theories, as is well known, have to square with
facts, not facts with theories, otherwise theories become a Pro-
crustean couch for scientific research. If, therefore, we find higher
laws governing animate nature than the purely physico-chemical
laws that govern inanimate matter, we must not deny the existence
of these vital laws, through love of any monistic dogma.
If in the psychical phenomena of animal life we find a higher
law than purely mechanical and physiological response to stimulus,
we must not deny the existence of the psychical life of animals,
through love of any monistic assumption.
And if, finally, in the spiritual life of man we find a higher law
than in the sensitive life of animals, which sensitive life, in the case
of man, forms only the foundation for his spiritual life with its in-
telligent thought and free will — we must not deny the existence of
the human spirit, through love of any dogmatic postulate of monism.
To do so would be absolutely unscientific !
In the second place the monistic assumption that in all nature
only one law can prevail, and that this law must fundamentally be
purely mechanical, is more than mere dogmatism ; it is concealed
materialism, decked out with Haeckel's ' atomic souls,' in order to
render it more attractive to superficial thinkers.
We have now advanced another step towards understanding
what is hidden under the catch-word ' monism.' As I said before,
MONISM 519
the literal meaning of monism is ' doctrine of unity,' or of the One.
This is what we must now examine, the kernel in the shell of monism.
As a doctrine of unity, monism is sharply contrasted with
dualism of every kind. It not only insists upon there being one sole
law governing the evolution of the world, but also upon there
being one sole substance. For this reason the monist regards spirit
and matter as essentially one, as merely different manifestations of
one and the same thing. For the same reason he believes God and
the world to be substantially one, for this is the logical outcome of
the monistic dogma of unity.
What must we think of tnis twofold postulate of dogmatic
monism ? It converts monism, the apparently harmless doctrine of
unity, first into concealed materialism, and secondly into concealed
atheism.
First into concealed materialism. The monistic theory of
identity,i which sees in body and soul nothing but two manifesta-
tions of the same thing, boasts of not being called materialism, but
nevertheless inwardly it does not differ from materialism, for
it regards what is psychical only as an unreal, subjective reflexion
of the material cerebral processes (Forel), and denies all causality
to psychical phenomena. It believes all causality to belong to the
material phenomena that accompany the psychical. But where
there is no longer any causality, there ceases also to be any reality,
and the psychical becomes a mere shadow of the material. This
amounts simply to the old materialism dressed up in a new fashion !
Secondly, we come to f^ ^ Qm'af m. If! ATI t.ifi pflflgj^^fol n.n ^ the
world, that aims at banishing the idea of a personal Creator, which
is said to be out of date. In the course of thousands of years,
pantheism has presented mankind with its doctrine of the One
under many different forms, .but none has approached atheism so
closely as HaeckePs new monism. There is absolutely nothing in
this monistic conception ol God. It is an empty nut, of which
the shell consists of the phrase ' the true, the good, and the beautiful '
— that new monistic * trinity,' as Haeckel called his new God. No
less a man than Caprivi openly declared that what was known as
monism was simply atheism, and Caprivi was assuredly not a
Jesuit !
The inward emptiness of the new monistic conception of God
must be obvious to every thoughtful human being. The God of
Haeckel's monism is nothing but a shadow of the world, reflected
in the cerebral functions of man, the highest vertebrate ; just in the
same way as in monistic psychology the spirit of man is a mere
shadow, a reflexion of the material working of his brain. There
1 This theory of identity and the whole psycho -physical parallelism of
monism have been sharply criticised by two eminent German psychologists,
K. Stumpf and L. Busse. Cf. on this subject my own work : * Die psychischen
Fahigkeiten der Ameisen, mit einem Ausblick auf die vergleichende Tier-
psychologie ' (Zoologica, No. 26), 2nd ed., Stuttgart, 1909.
520 INNSBRUCK LECTURES
is nothing underlying this conception, in spite of all the fine phrases
of the preachers of the new monistic religion.
You will, perhaps, reply that I am surely mistaken in saying that
monism is nothing but concealed atheism. Did not Professor Plp.tp.r
a member of the new German ' Monistenbund,' solemnly declare at
the discussion on February 18, 1907, his own personal conviction
to be that, if we assumed natural laws to exist, we must also assume
the existence of a lawgiver behind those laws ? Such a confession
is certainly not atheistic !
Plate actually used these words, and his anima naturaliter
Christiana revealed itself in them. I scarcely believed my ears
when I heard them, and I made a note of them at once for use
in my closing speech, in which I drew attention to the fact that,
to my great joy, Professor Plate, a member of the ' Monistenbund,'
had that evening publicly declared himself an adherent of Chris-
tianity, for a law-giver behind the laws of nature was precisely the
personal Creator of Christianity.
A week later, in the course of a lecture delivered in Berlin by
Pastor Steudel, of Bremen, who was then president of the ' Monisten-
bund,' a public rebuke was administered to Professor Plate for
this confession of theism. He submitted to the imperious order of
the monistic ' Congregation of the Index,' and withdrew what he
had said, by appending a note in the printed version of his address
to the effect that by these words he had, of course, only referred
to ' a lawgiver in the pantheistic sense.'
No logic, not even monistic logic, can justify such a statement !
P According to the pantheistic conception of God, the lawgiver is
I identical with the laws of nature, therefore it is impossible for him
to be ' behind them.' There is a flagrant contradiction in this
/ monistic trick of hiding a lawgiver somewhere behind the natural
laws, who, after all, turns out not to be behind them ! It is pitiable
to juggle in this way with words, and it is not creditable to the
German people. Either let a man frankly acknowledge himself
to be an atheist, or let him declare himself a theist, and an adherent
of Christianity !
My last words are addressed to the students. — Gentlemen, if
ever you have to encounter the perils of modern monism, remember
that it behoves you to fight for freedom against the unscientific
spiritual slavery of monism. One of my Berlin opponents, Professor
Dahl, showed his courage and his love of truth some months later,
when, in an article contributed to the Berlin Naturwissenschaftliche
Wochenschrift for 1907, No. 40, he wrote these words : ' Where
is then this freedom for science ? I shall be told that in our country
science and its teaching are free. They may be so in theory, but
those who have to watch over the maintenance of this principle
are but men. Adherents of monism have practically power of
nomination to all appointments in the department of zoology.
What is more natural than that they should nominate only those
CHEISTIANITY THE ONLY TKUE MONISM 521
who are not opposed to monistic doctrines ? I am far from sug-
gesting that there is any mala fides in question. The men who have
to propose names of suitable candidates honestly believe that
none but their own views can further the interests of science.
Therefore I ask again : where is freedom for science ? '
Gentlemen, here we have a free utterance on the part of a free
German ! Be yourselves free, whether you are Germans or not.
Take as your example the heroic struggle for freedom made by
the men of Tyrol in 1809. Just as they would not submit to
the tyrannical yoke of the Corsican, and remained loyal to their
hereditary rulers, so may you declare : ' We will not submit to
the unworthy yoke of intellectual slavery which modern monism is
seeking to impose upon us ! We will abide by our ancient Christian
faith loyally and without wavering ! '
Yes, Christianity, the old Christian theory of the universe,
that is now so often denied, furnishes us with the only true monism,
the only true doctrine of unity. There is one infinite and eternal God,
whose creative power produced all finite beings and preserves
them in existence. There is one God and one truth ! Yes, gentle-
men, there is only one truth, for from the inexhaustible source of
everlasting, uncreated truth flow two streams, that of natural
knowledge and that of supernatural revelation. Therefore there
can never be a real antagonism between knowledge and faith,
because there is only one truth which cannot contradict itself.
For this reason cling with loyalty and courage to your ancient
Christian faith !
Before we proceed to the discussion, I venture to make two
remarks.
1. Several years ago Professor Blaas, whom I esteem very
highly, lectured here on the origin of man. His views were
criticised in the press, and the Innsbrucker Nachrwhten published an
article on the descent of man, which went rather too far, and con-
tained several misleading statements. One of my colleagues re-
quested me to send him materials for a refutation, and I referred
him to an address on the subject of fossil man, delivered by Professor
Branco at the fifth International Congress of Zoologists at Berlin
in 1901. I had quoted the shorthand report of this address in my
' Modern Biology and the Theory of Evolution,' and my colleague
mentioned this quotation in one of the Catholic papers published in
this town. Thereupon, in another Innsbruck paper, the now
unfortunately defunct Tiroler Tageblatt, I was accused of having
intentionally distorted the meaning of Branco's words. I wrote
to him at once to Berlin, and asked him to let me know whether the
passage in question had been correctly reproduced by me or not.
Professor Branco replied that what I had written down whilst he
was speaking agreed completely with what he had been saying, but
at the present time he should alter a few words in it. He had,
522 INNSBKUCK LECTUEES
however, really intended to check the tendency to go to extremes.
And now people come and accuse me of forgery ! I have no desire
to be classed with Haeckel !
I feel bound on this occasion to declare explicitly that Professor
Blaas has assured me that he was not concerned, either directly or
indirectly, with the charge brought against me in the Tageblatt.
I wish to make this publicly known, for I am a lover of truth.
2. An article by Dr. Franz von Wagner appeared some years ago
in the Zoologisches Zentralblatt, in which he discussed my ' Modern
Biology and the Theory of Evolution.' He acknowledged the value
of the scientific sections in which fresh evidence in support of the
theory of descent was adduced from guests among ants and termites,
my special department of research ; but wherever my line of
argument did not please him, he remarked : ' You are under
theological influence,' and in this way he easily avoided any attempt to
refute me. Professor von Wagner must not be offended if I advise
him to adopt another line of argument next time. If by personal
union, to employ an expression that must be very familiar here in
Austria, a man is first a zoologist, then a philosopher, and only in the
third place a theologian, it is surely unfair for that reason to cavil
at what he says on natural science and philosophy, and for want of
a better argument to keep on repeating that he is a theologian.
The first thing to do is to show that theological prejudices have
influenced me in stating the results of my scientific or philosophical
investigations. This remark completes what I have to say . . .
and I have only to offer you all, and especially the Catholic students,
my most hearty thanks for your attention.
1 This writer must not be confused with Dr. Adolf Wagner, professor to
Innsbruck, to whose work on Lamarckism I have referred on p. 493.
SUPPLEMENTARY NOTES
ON CHAPTER I, p. 5.
THE Kev. John Gulick in his book c Evolution, Kacial and Habitu-
dinal ' (Carnegie Institution, Washington, 1905), p. 9, defines bionomics
in the following words : ' Bionomics is the science that treats of
the origin of organic types, and of the relations in which they stand
to each other and to the physical environment.' For this definition
he refers to Sir E. Kay Lankester's article on Zoology, in the ' En-
cyclopedia Britannica,' ninth edition. This definition, however,
includes the theory of evolution (biogeny), which does not, in my
opinion, belong to biology in the restricted sense.
ON CHAPTER VI, P. 110, NOTE 2, AND P. 169.
On the subject of the accessory chromosomes see also H. Otte,
' Samenreifung und Samenbildung bei Locusta viridissima, I '
(Zoologischer Anzeiger, XXX, 1906, Nos. 17 and 18, pp. 529-535).
ON CHAPTER VI, PP. 130, &c., AND P. 134.
On the subject of the conjugation of unicellular organisms
see also E. Korschelt, ' t)ber eine eigenartige Form der Fortpflanzung
bei einem Wurzelfiisser, Pelomyxa palustris' (Naturwissenschaft-
liche Rundscha^XXI, 1906,No. 38, pp. 503, 504). This little creature,
which resembles an amoeba, has a complicated method of pro-
pagating itself. Numerous gametes are formed within the mother,
and subsequently swarm out, and unite in pairs to produce a new
individual. At the formation of the gametes, a reduction-division
of the chromosomes takes place. The nuclear spindles of the
mitotic figures are the result of a division of centrosomes that are
very plainly visible.
ON CHAPTER VI, P. 138.
On the subject of parthenogenesis in plants see also 0. Rosen-
berg, l Uber die Embryobildung in der Gattung Hieracium '
(Berichte der deutschen botanischen Gesellschaft, XXIV, 1906, pp.
157-161).
523
524 SUPPLEMENTAL NOTES
ON CHAPTER VIII, P. 213.
Closely connected with experiments on the regeneration of
missing parts of an animal are experiments in transplantation, in
which a piece of another animal is grafted on to supply the place
of what has been amputated, and the results of the operation are
carefully observed. These experiments are very instructive and
throw light on the problem of determination. On this subject two
very interesting papers were read on September 20, 1906, at the
seventy-eighth meeting of German Naturalists at Stuttgart — ' XJber
embryonale Transplantation,' by H. Spemann, and ' X)ber Regenera-
tion und Transplantation im Tierreich,' by E. Korschelt. (Cf.
Naturwissenscha/tliche Rundschau, 1906, No. 41, &c.)
ON CHAPTER IX, P. 303.
That the doctrine of evolution as a theory in natural science
is perfectly compatible with the Christian cosmogony has been
repeatedly pointed out by Protestants also. Cf. Dr. Rudolf Schmid,
* Das naturwissenschaftliche Glaubensbekenntnis eines Theologen,'
second edition, Stuttgart, 1906, and E. Dennert, ' Bibel und
Naturwissenschaft,' fifth edition, Stuttgart, 1906.
To illustrate p. 12 1 etc.
Plate I.
Diagrammatic representation of the process of fertilizing an egg-cell (after Boveri).
See p. 121 etc.
To illustrate pp. 172, 173.
Plate II.
J
(?)
3 (A+a)
The Chromosome Theory and Mendel's Law of Hybridization (after Heider).
(The red chromosome A indicates a tendency to produce red blossoms; the red-edged chromosome
a indicates a tendency to produce white blossoms; $ = male germ-cell; $ = female germ-cell.)
Fig. i and 2. Nuclei of the parent germ-cells of varieties with red and white blossoms respectively.
Fig. 3. Union of these nuclei in the cells of the first generation of hybrids.
Fig. 4 and 5. Distribution of the chromosomes at the maturation-divisions of the germ-cells of
the first generation of hybrids.
Fig. 6 — 9. Combination of the chromosomes in the cells of the second generation of hybrids.
To illustrate pp. 348 — 364.
Plate III.
Doryloxenus transfugaWasm. (East Indies.)
12 times the natural size.
Forefoot and tip of tibia of Doryloxenus.
500 times the natural size.
Claviger testaceus Preyssl. (Europe.
12 times the natural size.
Pselaphus Heisei Hbst. (Europe.)
[2 times the natural size, t — maxillary palpi.
Paussiger limicornis Wasm. (Madagascar.)
12 times the natural size.
Miroclaviger ceruicornis Wasm. (Madagascar.
12 times the natural size.
To illustrate pp. 364—379.
mte IV
Pleuropterus brevicornis \Vasm. (Bagamoyo.)
3 times the natural size.
Pentaplatarthrus natalensis Westw. (Natal.)
4 times the natural size.
Lebioderus Goryi Westw. (Java.)
6 times the natural size.
Pa,2issus howa Dohrn. (Madagascar.
4 times the natural size.
Paussus spiniceps Wasm. (Sierra Leone.)
6 times the natural size.
Paussus dama Dohrn. (Madagascar.)
6 times the natural size.
To illustrate pp. 37 — 44 and 379 — 386.
Plate V.
Stenogastric imago of Tennitojcenia. As smut hi
Wasm. (East Indies.)
16 times the natural size.
(ap = appendages on the thorax, taking the
place of the front-pair of wings.)
2
Stenogastric imago of Termitoxenia (Termito-
myia) mirabilis Wasm. (Natal.)
16 times tlie natural size,
(ap = appendages on the thorax, as in Fig. i.)
Physogastric imago of Termitoxenia Assmitthi
Wasm. (East Indies.)
16 times the natural size.
(s = point of the abdomen.)
4 5
Thoracic appei.dage of Thoracic appendage of
a physogastric imago of a physogastric imago of
Term. Heimi Wasm. Term. Assmitthi Wasm.
(East Indies.) (East Indies.)
1 1 5 times the natural size. 115 times the natural size,
(p, p = exudatory pores (p, p = exudatory pores
on the hinder branch ) on the hinder branch )
To illustrate pp. 445 and 462.
Plate VI.
A. Human skeleton.
An adult Frenchman, 30 years of age.
1.727 m. in height.
Humerus 28 cm. Femur 47 cm.
Ulna 25 cm. Tibia 37 cm.
Radius 22 cm.
B. Skeleton of an adult Orang-utang.
(Simia satyrus L.) 1.60 m. in height.
Humerus 36 cm. Femur 31 cm.
Ulna 41 cm. Tibia 25 cm.
Radius 39.8 cm.
To illustrate pp. 445 and 462.
Plate VII.
To illustrate p. 511.
Plate VIII.
INDEX
Acanthotermes, 351
Achromatin, 01 etc.
Actinosphaerium, 99, 134
Adaptation, characteristics due to,
295, 317, 327, 329, 337, 341,
350, 361, 364, 373, 382, 427,
487, 492
Adipose tissue and true guest-relation-
ship, 44, 76, 338, 362
in Termitoxeniidae, 39,
51, 54, 380
Adoption colonies of ants, 393 etc.,
395 etc., 407, 417 etc., 420,
423
Aenictus, 350
Aequorea, 121
Africo-Indian continent, 356, 359
Agamous propagation, 160, 163
Albert the Great, 11-16
Albumen, 196, 197
Alchimilla, parthenogenesis, 138
Akocharinae, 322, 337, 340
Allantois, 456
Allied colonies of ants. See Colonies,
mixed
Allometrosis among ants, 397
Alpine salamander, 454
Alveolar theory, Biitschli's, 57
Amazon ants. See Poly erg us
Amber, insects in, 276, 329, 369, 373,
390, 415
Ametabolia. See Metamorphosis
Amical selection, 331, 338, 339, 379,
493
Ammonites, 299
Amoeba, movements, 71
merotomy, 80
Amphibia, embryological experi-
ments, 228 etc.
maturation divisions, 113
See also Frog, Triton
Amphimixis, 108, 139
significance of, 146, 163,
175
Amphioxus, 222, 235, 447
Anatomy, 6
development of, 25 etc.
Ancestors of man, according to Dubois,
465, 504
Haeckel, 446, 476,
512
Klaatsch, 463, 466
Kollmann, 475
Schwalbe, 468, 471,
505
Wiedersheim, 443
and palaeontology, 463 etc.,
477 etc.
Anergates, 387, 408, 410, 417
Angiosperms, double fertilisation, 128
See also Xenia
Animal system of Albert the Great,
11-16
Aristotle, 10 etc.
Hippocrates of Cos,
9
Linnaeus, 18 etc.
Annelida, experiments with eggs, 144,
234
Anomma, 340, 349, 353, 357
Ant-beetles. See Paussidae
Ant-inquilines, 44, 76, 315 etc., 327 etc.
See also Cetonia, Chitosa,
Dinarda, Lomechusini, Myrme-
chusa, Myrmedonia
Ants, number of chromosomes, 93
palseontological evolution, 276,
329, 390, 411
parthenogenesis, 135, 422
slavery among, 386 etc.
systematic classification, 309
etc.
wandering, 340 etc., 350
See Aenictus, Anergates, Anom-
ma, Aphaenogaster, Atta, Bothrio-
myrmex, Camponotus, Dorylus,
Eciton, Epipheidole, Epoecus, For-
mica, Formicoxenus, Ldbidus,
Lasius, Leptothorax, Monomorium,
Myrmica, Myrmoxenus, Pheidole,
Polyergus, Stenamma, Strongy-
lognathus, Symmyrmica, Sym-
pheidole, Tapinoma, Tetramorium,
Tomognaihus, Wheeleria
526
INDEX
Antedon, crossed with Echinus, 152
Antennae of Clavigeridae, formation
of, 360 etc.
of Paussidae, biological
significance of,
375 etc.
joints in, 364 etc.
modification of,
367 etc., 374,
etc.
Aniennaria, parthenogenesis, 138
Anthropology, 5, 432 etc.
Ape-man. See Pithecanthropus
Apes, blood-relationship of, 457, 503
fossil, 463, 464
placental formation, 456, 502
skeleton of, 445 etc., 501
skull of, 445 etc., 501
theories regarding relation of
man to, 258, 456 etc., 462
etc., 500 etc.
Aphaenogaster, 323 etc.
Aphididae, 135, 420
Apoderiger, 363
Apogamy, 138
Arenicola, blood reaction in, 458
Aristotle, 9, 104, 141, 158, 456
Arrhenogenesis, 138, 150
Artemia, alleged transformation of,
314
number of chromosomes, 93
parthenogenesis, 137
Arthropterus, 369, 372, 378
Ascaris, cleavage of eggs, 221, 223
germ and somatic cells, 122,
124, 167, 237
number of chromosomes, 92,
93, 175
process of fertilisation, 121
reduction of chromosomes,
113
A .scares-type of fertilisation, 121,
123, 156, 167
Ascidia, experiments with eggs, 234,
245 etc.
Asplanchna, egg-cleavage, 221, 222
Atavism, 385, 452
Atemeles, 330 etc., 334 etc.
emarginatus, 332
paradoxus, 332, 334
pratensoides, 335 etc.
pubicollis, 334, 335
Atta, 345
Attonia, 346
Augustine, St., remarks bearing on
evolution, 274
on creation, 437 etc.
Australia, early types preserved in,
277
Autoblasts, 191, 199
Autonomy of the nuclear substance,
167
vital processes, 108,
243
Autoplasson, Haeckel's, 196
Bacillus BiitscUii, 49, 183
Bacon, Roger, 16
Bacteria, 49, 182
von Baer, K. E., founder of em-
bryology, 28, 209
on the perception of the
spiritual, 435
theory of germinal layers,
28
BaihyUus, 181, 196
Batrachoseps, chromatin thread, 65
Bees, Vergil's belief in spontaneous
generation of, 200
Beetles, ant- and termite-inquilines,
44, 76, 315-379
number of species, 20
Beggiatoa, 183
Bioblasts, 190, 192
Biochemical branches of industry, 76
Biogenesis, Oskar Hertwig's theory of,
192
Biogenetic law, 446 etc., 487, 502
Biogens, 190
Biology, comparative, 28
earliest development of, 8 etc.
meaning and subdivisions of,
3 etc.
of inquilines among ants and
termites, 327 etc.
and spontaneous generation,
178 etc., 200 etc.
and vitalism, 21 1 etc., 238 etc.
Biometry or statistical biology, 5
Bionomics, 5, 523
Biophors, Weismann's, 107, 176, 190
Bireduction division, 112
Blastem theory, Robin's, 201
Blastoderm formation in insects, 202
Blastomeres, 119, 123, 208, 220, 231,
233
Blastula, 222, 231, 234, 237, 244
Blattinae, 277
Blepharoplasts, 100
Blood, chemical reaction of, 457 etc.
corpuscles, mode of division, 87
non-nucleate, 185
red, 77
white. See Leucocytes
Blood-relationship between man and
apes, 457 etc., 503
Blood-tissues in insects, 76
in termite-inquilines, 38,
76, 384
INDEX
527
Bombyx, parthenogenesis, 137
Botany, 7
growth of systematic, 17, 22
Boihriomyrmex, 387, 415
Brachystola, 110, 170
Branchial clefts and arches, 453 etc.,
503
Branchipus, 175, 314
Bryophyta (Mosses), 99
Butterflies, parthenogenesis in, 135
CAENOGENESIS, Haeckel's theory of,
449
Caloptenus, maturation divisions in,
115
Calotermes, 277
Campodea, 39
Camponotinae. See Formicinae
Camponotus, host of Mirodaviger, 363
Xenodusa, 330
species and subspecies, 310
maculatus, 310
pennsylvanicus, 331
pictus, 331
Cancer pagurus, blood-reaction, 458
Carabidae, connected with Paussidae,
365, 369
termitophile, 76
Carabus, 19, 310
Carbon theory, Haeckel's, 195
Carcharias, placental formation, 456
Catastrophe, Cuvier's theory of, 275
Caulerpa, cells of, 53, 54
Cells, definitions of, 32 etc., 48
discovery of, 30 etc.
division of, 85 etc.
form and size of, 49 etc.
lowest units of organic life, 55
etc., 66 etc., 179-193
membrane of, 32, 63
morphology of, 63-65
nucleus. See Nucleus
with one and several nuclei, 53
organisation of, 67 etc., 180 etc.
products of, 75
structure of, 54 etc.
Cell-plate, 95, 97
Cellular bridges, 51, 75, 187
life, 66 etc.
physiology, 46, 102
Cellulose, 75, 80, 97
Centrosomes, 56, 65, 90, 96, 98, 122,
126
in artificial parthenogenesis
and merogony, 142, 146,
154, 157
in Protozoa, 99, 134, 523
See also Spermatocentro-
somes
Cerapterus, 365, 378
Ceratoderus, 366, 371
Cetonia cocoons or ant-stones, 200
Chaetopisthes, gland-cells in wing-
sheaths, 58
Chaetopterus, artificial partheno-
genesis, 141
Chemical composition of albumen, 196
of nucleinic acid, 196
of protoplasm, 33
Chimpanzee, blood reaction, 458
cranium of, 467, 469
Chironomus, paedogenesis in, 135
Chitosa, phylogenetically connected
with Dinarda, 322
Chlorophyll, 71, 75
Chromatin, 61 etc., 80 etc. See
Chromosomes
as material substance of
heredity, 84, 191, 213,
236 etc.
diminution, Boveri's,
123
reduction, in germ-cells,
110 etc.
in conjugation, 523
in merogony, 150
etc.
in parthenogenesis,
136 etc., 144 etc.
significance of, 164
etc.
Chromatophores, 49, 75
Chromidia, 49, 180, 183 etc.
Chromioles, 65
Chromomeres, 65, 168, 175, 183
Chromosomes, 65
accessory or heterotropic,
92, 110, 170, 523
bearers of heredity, 84, 125,
135, 159, 167, 191, 213,
236, 247
bearers of laws of organic
development, 169, 177,
247
behaviour in artificial par-
thenogenesis, 143
etc.
in conjugation, 130
in merogony, 150
in merotomy, 80 etc.
in natural partheno-
genesis, 136 etc.
in normal fertilisation,
120-125
differential and integral
division of, 236, 237
individuality of, 117, 167,
168
not vital units, 187
528
INDEX
Chromosomes — continued
number in various animals
and plants, 92, 93, 175
qualitative difference in,
169
reduction in germ-cells, 110,
156
regular distribution ' of , 97,
101
relation to Mendel's Laws,
171
Ciliata, 74, 130
Clathrotermes, 277
Clavellina, Driesch's experiments, 245
etc.
Claviger, 360
Clavigeridae, characteristics due to
adaptation, 360 etc.
phylogeny of, 362 etc., 428
See Apoderiger, Claviger, Miro-
daviger, Paussiger
Cleavage-nucleus of the ovum, 119
etc., 129, 219
Cleavage, process of, 119 etc., 122,
208 etc.
Cleavage-spheres or corpuscles, 119
etc., 142, 219
Cleavage-spindle, 121 etc.
Coccidiidae, mode of propagation, 133
Collective types, 277
Colonies of ants, mode of forming, 391
etc.
mixed or allied, 392
etc.
simple, 391
of unicellular organisms, 132
etc.
Conjugation of Infusoria, 130 etc., 160,
163, 523
Convergence, phenomena of, 343, 457
Copepoda, maturation -divisions, 114
parasitic degeneration,
327, 454
Copernican cosmogony, 272, 427, 482
Copulation nucleus in Infusoria, 131
Correlation, Cuvier's Law of, 28
Cosmogony, Copernican, 272, 427, 482
Darwinian, 257, 265, 300
monistic, 205, 267, 277,
300
Ptolemaic, 272, 482
theistic, 205, 299, 427, 481
Cosmology, 3
Crab, blood-reaction, 458
Crania of men and apes, 465, 507 etc.
Macnamara's curves,
469 etc.
Cranial capacity, 471 etc., 508
Creation of first organisms, 194, 204,
280, 299 etc.
Creation of human soul, 283 etc., 436
etc.
of man, according to St.
Augustine, 437 etc.
of matter, 194, 280
Creation, theory of, a postulate of
science, 205 etc., 268, 299 etc.
and theory of
evolution, 277
etc., 299 etc., 302
etc., 427 etc.
Crepidula, egg-cleavage, 222
Cross-breeding and heredity, 173
among plants, 313
among species of Atemeles,
335
Mendel's Law concerning,
170
of Echinus with Sphaer-
echinus, 151 etc.
with Strongylocen-
trotus, 154
with Antedon, 152
Crustacea. See Artemia, Branchipus,
Cancer, Copepoda, Cypris, Ler-
naea, Mollusca, Phyllopoda,
Rhizocephala
Cryptogams, conjugation, 131
Ctenophora, experiments on, 233 etc.
Cubitermes, host of Pygostenus ter-
mitophilus, 357
Cuvier, 27 etc.
Cyanophyceae, 182 etc.
Cypris, parthenogenesis, 136, 139
Cystoflagellata, centrosomes, 134
Cystosira, merogony, 149
Cytoblastema theory, Schwann's, 201
Cytodes, Haeckel's, 185
Cytolpgists, recent, 45 etc.
Cytology, 6
early history of, 29 etc.
further development of, 46,
48 etc.
Schwann-Schleiden's work
in, 32
survey of the growth of, 63
etc.
Cytomitom, 57
Cytoplasm, 57 etc., 82 etc.
DARWINISM, meanings of the word, 256
etc., 489 etc., 494 etc.
criticism of, 259 etc., 443
etc., 494 etc.
Defective cleavage, 234
Deluge, the, and geology, 274
Descent of man, 258, 266, 430 etc., 496
etc.
evidence of, 443 etc.
INDEX
529
Descent of man — continued
theories regarding,
456 etc., 462 etc.
Descent, theory of, 255, 430 etc.
or theory of perman-
ence ? 307-429
Determinants, 107, 176, 192
Determination, problem of, 108, 209
etc., 218 etc.
conclusions regarding,
235 etc.
experiments in, 222 etc.
Deuteroplasm, 52, 202
Development,geological and biological,
of our earth, 272 etc., 427
etc.
imaginal, of Termitoxenii-
dae, 39 etc., 380 etc.
See also Cleavage, Evolution,
Fertilisation
Diapedesis, 72
Diatomaceae, 75
Differentiation, dependent or inde-
pendent ? 212 etc. See Deter-
mination
Dimorphism, seasonal, 314
Dinarda, 250, 315 etc.
evolution of, 315-326, 426
Dinardini, phylogenetic connexion
between, 321, 323 etc.
Diptera. See Chironomus, Eristalis,
Miastor, Musca, Phoridae,
Termitoxeniidae
Discoxenus, phylogenetically con-
nected with Doryloxenus and
Termitodiscus, 353 etc.
Dixippus, parthenogenesis, 139
Dolichoderinae, 415
Dominants, Reinke's, 108, 177, 243
Dorylinae. See Aenictus, Anomma,
Dorylus, Eciton, Labidus
inquilines among, 340 etc.,
348 etc.
Dorylomimus, 341, 347
Dorylostethus, 347
Doryloxenus, as ant-inquiline, 344, 349
as termite-inquiline, 349
etc., 426
Lujae, 344, 349
termitophilus, 352
trans fuga, 351 etc.
Dorylus, 340, 349
Double fertilisation in Angiosperms,
128
Dytiscus, 169, 237
ECHINODERMS, experiments on eggs,
231, 244 etc.
Echinus, artificial parthenogenesis, 140
Echinus — continued
embryological experiments,
231, 244
merogony, 149 etc.
number of chromosomes, 93
process of fertilisation, 119
etc.
size of egg, 120
superfecundation, 128
See also Cross-breeding
Echinus-type of fertilisation, 120,
125, 156, 167
Eciton, 340 etc.
Burchelli, 342, 343
coecum, 342
Foreli, 342
praedator, 340, 342 etc., 348
quadriglume, 342
Eciton inquilines, 341 etc.
Ecitonidia, 341
Ecitophya, 341, 347
Ectocarpus, male parthenogenesis, 138
Ectoderm, 222
Ectrephidae, myrmecophile beetles,
329
Egg-cells, and the problem of deter-
mination, 228
maturation-divisions, 109-
119
normal fertilisation, 119 etc.,
162
of Termitoxenia, 38 etc.,
50, 52, 382 etc.
parthenogenetic fertilisa-
tion, 135 etc., 139 etc.
size of, 52, 120
Egg-cleavage, 119, 122, 208
governed by preformation
or epigenesis, 211 etc.
types and varieties of, 208
etc.
embryological experiments
in, 228 etc.
Eggs, experiments in merogony, 149
etc.
holoblastic and meroblastic,
208
telelecithal and centro-
lecithal, 209
Elementary organisms, fictitious, 59
Elodea, flow of protoplasm, 74
Embryology, 7, 28
Embryonic development, cause of,
126 etc.
of man, 455 etc.
Embryos, Haeckel's illustrations of,
513
Encyrtus, polyembryony in, 135
Endosperm, 129
Energids, 189
2 M
530
INDEX
Energy, law of mechanical, 242
Entelechies, 108, 178, 206, 238, 243
Entoderm, 222
Eolithic theory, Rutot's, 509
Ephebogenesis, 150
Epigenesis, 108, 209 etc., 218 etc., 225
etc., 235
Epipheidole, 407, 415
Epoecus, 407, 415
Equation-division, 111, 117
Equatorial plate, 95, 97, 117
Equidae, hypothetical phylogeny of,
275, 298
Eristalis, 200
Ethology, 4
Eudorina, mode of propagation, 132
Eumitotic maturation-division, 111,
112, 115 etc.
Eutermes. See Cubitermes
Evolution, laws governing, of Dinar-
dini, 323 etc.
of Dorylinae inquilines,
347 etc.
of Lomechusini, 337 etc.
of Paussidae, 373 etc.
of termitophile Aleochari-
nae, 354 etc.
of Termitoxeniidae, 382
etc.
Evolution, laws of, cosmic, 273 etc.
interior, 176 etc., 220, 247,
263, 270, 283, 297, 303,
312, 324, 348, 372 etc.,
385, 492
mechanical, 241 etc.
organic, 169, 176 etc., 269
etc., 492
in relation to the
chromatin of the germ-
cells, 176 etc., 236 etc.,
247, 297
vital, 241-249
Evolution, theory of, 250 etc., 486 etc.,
496 etc.
and Copernican theory,
272, 427
as a scientific theory, 267
etc., 285 etc., 486 etc.
evidence supporting, 312
etc., 327 etc., 487 etc.,
498 etc.
philosophical limits of,
279, 488
subject-matter of, 486 etc.
and Darwinism, 258 etc.,
489 etc.
and the Christian cosmo-
gony, 267, 279, 299 etc.,
304, 427, 481 etc., 486
etc., 494 etc.
Evolution, polyphyletic or mono-
phyletic? 255, 271, 293, 297,
303, 487, 497, 499
of ants and ant-inquilines. See
Ants
of apes, 464
of man, according to Dubois,
465, 504
Haeckel, 446 etc., 476,
502, 512
Klaatsch, 462 etc., 502,
507
Kollmann, 475
Kramberger, 472 etc.,
506
Schwalbe, 468, 506
Stratz, 504
Wiedersheim, 443
of slavery amongst ants, 411
etc., 492
of the whalebone- whale, 452,
498
thoughts on, 250 etc., 486 etc.
various theories of, 262, 489
Exudation, organs of, in inquilines
among ants and termites, 38,
338, 361, 365, 366, 367, 370
etc., 374, 381
FAT, biological importance of, 76
Feeding of genuine ant-inquilines,
336, 338, 363
Fertilisation, abnormal, 127 etc., 149
etc.
Echinus and Ascaris types
of, 120 etc., 167
nature of, 119 etc., 127 etc.,
155 etc., 165 etc.
normal, 119 etc., 161 etc.
problem of, 104 etc., 155 etc.
process of, 119 etc., 155 etc.
teleological significance of,
160 etc., 163 etc.
theory regarding, Boveri's,
121 etc., 128 etc., 146 etc.,
160
twofold aim of, 126 etc.,
160 etc.
Filar theory of cytoplasm, 57
Flagellata, 74, 132
Flagelliform cells, 74
Flow of granules in cell, 71
protoplasm, 71
Foraminifera, 72, 75
Formica, host of Dinar da, 317 etc.
Lomechusa and Ate-
meles, 330 etc.
origin of slavery among,
392 etc., 411 etc., 420 etc.
INDEX
531
Formica — continued
simple and mixed colonies,
391 etc.
slave-keeping species, 387
etc.
aserva, 395
consocians, 392, 415, 417
dakotensis var. Wasmanni,
394, 395 etc.
exsecta, 392, 420
exsectoides, 392
fusca, 388, 391 etc., 394,
415 etc., 420 etc.
impexa, 392
incerta, 392, 415
microgyna, 392
montigena, 392
nepticula, 392
nitidiventris, 395
pallidefulva, 398
Pergandei, 394
pratensis, 335 etc., 391, 397,
422
rubicunda, 330, 395 etc.
rufa, 334, 391 etc., 417, 419
etc.
rufibarbis, 334, 388, 391,
399, 400
sanguinea, 330, 334, 392,
397, 413, 416, 421 etc.
subaenescens, 395 etc.
subintcgra, 396
subsericea, 395 etc.
truncicola, 392 etc., 412 etc.,
416-423
Formicinae (Camponctinae), 400, 413
etc.
Formicoxenus, 407
Free cellular formation, 186, 201, 202
Free nuclear formation, 186
Frog, experiments on eggs, 213, 217,
228 etc.
number of chromosomes, 93, 175
Fungi in ants' nests, 345, 346
GALL-FLIES, parthenogenesis, 135
polar bodies, 137
Galtonia, maturation-divisions, 116
Gastrula, 222, 234
Gemmae, Haacke's, 190
Gemmaria, Haacke's, 190
Gemmation, 86, 160
Gemmules, Darwin's, 190
Generatio aequivoca. See Spontaneous
generation
Geology, 252 etc., 274 etc., 427
Germ-areas, 123 etc.) 169 etc.
Germ-cells, 68 etc.
in fertilisation, 119 etc.,
156 etc.
Germ-cells — continued
maturation-divisions, 109
etc., 156
Germinal layers, von Baer's theory of
28
selection, 176 etc., 264, 493
Germ-plasm, 107, 123, 192
continuity of, 107, 123,
168 etc.
theory, 107, 161, 174, 192
Germ-regions for formation of organs,
216
Glia, Maggi's, 196
Gnostidae, 329
Granula, 59, 189, 191, 199
Granular theory, Altmann's, 59, 189,
199
Grasshopper, number of chromo-
somes, 93. See also Brachy-
stola, Caloptenus, Locustidae,
Orthoptera, Phasmidae
Green Algae, 132
Gromia oviformis, 71
Gryllotalpa, maturation-divisions, 114
Guest-relationship, 44
of Chaetopisthes, 58
of Clavigeridae, 360 etc.
of Lomechusini, 330 etc.
of Paussidae, 364 etc.
of termite-inquilines, 76
of Termitoxeniidae, 38 etc.,
379 etc.
HAECKELISM, 258, 265, 266, 268, 301,
495, 512
Haemosporidae, mode of propagation
133
Heidelberg, human remains found
near, 505 etc.
Hemiembryos, 228 etc.
Hemiptera, maturation-divisions, 1 14,
170 etc.
number of chromosomes,
175
See also Pyrrhocoris and
Syromastes
Heredity, 104 etc., 176 etc.
chromatin of nucleus special
bearer of, 83, 84, 97 etc.,
125, 135, 159 etc., 167 etc.,
171, 191, 213, 236, 247
Hermaphroditism, protandric, 40, 380
Heterochromosomes, 110, 170
Heterogony (see Fertilisation), 136,
494
Hieracium, crossing species of, 313
parthenogenesis, 523
Histology, 7, 8, 27, 30, 34
Histonal selection, Roux's, 203, 493
2 M 2
532
INDEX
Holothurians, fertilisation of, 149
Homo primigenius, 470 etc.
Homopterus, 370
Hyaloplasm (see Cytoplasm), 58, 59
Hybridisation, Mendel's Laws of, 170
Hydra, gemmation in, 86
Hydromedusae, experiments on eggs
of, 232
Hydrophilus, number of chromosomes,
93
Hylotorus, 366, 367, 371
Hymenoptera, polyembryony in, 129
Hypertely, 348
Hypothesis defined, 285
IDANTS, Weismann's, 107, 190
Idiochromosomes, 170
Idioplasm, Nageli's, 107, 124, 191
Ids, Weismann's, 107, 175, 190
Imago form of Termitoxeniidae, 39,
380 etc., 384 etc.
Indifferent type oWorylinae'mquilmes,
243
Individuality, meaning of, 67, 168,
187, 188
of chromosomes, Boveri's,
117, 167 etc.
Infusoria, conjugation, 130 etc.
merotomical experiments,
80 etc.
movements, 74
Insects, parthenogenesis, 137, 422
Intercellular bridges, 51, 75, 187
Interzonal fibres, 94-97
Intrinsic or self -differentiation, 211 etc.
of cleavage-cells,
218, 232 etc.
Isogamy, 160
JAVA, skulls found in. See Pithecan-
thropus
KABYOKINESIS, 87
stages in, 88 etc.
survey of, 97 etc.
Karyomitom, 61 etc.
Karyoplasm, 61 etc.
Kernplasmarelation, R. Hertwig's,
79, 162
Kinoplasm, 100, 162
Kircher, Father, on the evolution
of species, 276
,Krapina, human remains found at,
473 etc., 506 etc.
Lalidus, 342
Lamarckism. See Neo-Lamarckism
Laminaria, asexual propagation, 161
Laminariaceae, and the biogenetic
law, 449
Lancelot, 447. See Amphioxus
Lapis myrmeciis, 200
Lasius, host of Claviger, 360
number of chromosomes, 93
parthenogenesis, 137, 422
polar bodies, 137
Lelnoderus, 366, 368, 370, 371, 378
Lemuridae, blood-reaction in, 460
formation of hand, 462
fossil, 464
Leptothorax, 401, 407
Lernaea, 327, 454
Lernaeopoda, 327
Leucocytes, 72 etc.
Leucoma, parthenogenesis, 137
Life, shown in movement, 69
Lily, number of chromosomes, 93, 175
Limax, number of chromosomes, 93
Lingula, phylogeny of, 276
Linin, 61 etc.
Linnaeus, founder of systematic classi-
fication, 18 etc.
idea of species, 296
'Systema Naturae,' 18, 23
Liparis, parthenogenesis, 137
Litomastix, polyembryony, 129, 135,
137
Locusta, 523
Locustidae, 114
Lomechusa, 330-340
Lomechusini, 298, 330 etc. See Ate-
meles, Lomechusa, Xenodusa
Lug-worm, blood-reaction, 458
Lycosa, spermatogenesis, 170
Macacus, blood-reaction, 457
Machine theory of life, 238-249
Macrogametes, 133
Macrogonidium, 132
Macronucleus in Infusoria, 130 etc.
Madagascar, antennae of beetles in,
363
Maize, xenia in, 129
Malaria parasites, 133
Man, creation of, 283 etc., 436 etc.
fossil, 467 etc., 477 etc., 504 etc.
number of chromosomes, 93
races of, 468 etc., 473 etc., 477
etc., 510 etc.
See also Creation and Evolution
Marsupials, 447
Mastotermes, 277
Maturation-divisions of germ-cells,
109 etc., 156
Boveritype, 112
eumitotic type, 111 etc.
INDEX
533
Maturation-divisions of germ-cells —
continued
in parthenogenesis, 135
etc.
Korschelt type, 114
pseudomitotic type, 111
etc.
Weismann type, 113,
114
Mechanics of development, 211, 221,
238-249
Medusae, number of chromosomes, 93
Mendel's Law of Hybridisation, 170
etc.
Merismoderus, 366, 371
Merocytes, 128
Merogony, 149 etc.
Merotomy, 80 etc., 228 etc.
Mesoderm, 222
Metakinesis, 494
Metamorphosis, 7
absence of, in Termito-
xeniidae, 38, 381 etc.
Metastructural parts, Roux's, 190
Miastor, paedogenesis, 135
Micellae, Nageli's, 190, 191
Microgametes, 133
Microgonidium, 132
Micronucleus of Infusoria, 130 etc.
Micropyle, 127
Microscope, invention of, 29
improvements in, 31, 45
etc.
sections for, 41
Microsomes, 60, 100
Microtome, 36, 37, 41, 42
Migration, theory of, 493
Mimeciton, 340 etc.
Mimetic type of inquilines, 328, 340
etc., 347 etc. See also Dory-
lomtmus, Dorylostethus, Ecito-
nidia, Ecitophya, Mimeciton
Mind of man, 284 etc., 441 etc.
Mirabilis Jalapa, 172
Miroclamger, 363
Mitosis. See Karyokinesis
Mitrocoma, fertilisation, 122
Molchmaus, 501
Mollusca, experiments on, 234 etc.
Monera, 181 etc.
Monerula stage in human ontogeny,
215, 447
Monism, criticism of, 205, 255, 258,
265 etc., 267, 277, 300 etc.,
495, 515 etc.
Monistic idea of God, 205, 300, 513
Monomorium, 405 etc., 410, 415
Monophyletic evolution. See Evolu-
tion
Monorrhina, 447
Monotremata, 277, 456
Morphogeny, 3, 6
Morphology, 3, 6, 26 etc., 498
comparative, of ant- and
termite-inquilines, 327
etc.
of the cell, 48-65
Mosaic theory, 225 etc. See also Deter-
mination
Mouse, number of chromosomes, 93,
175
le Moustier, human remains found at,
506, 507, 509, 511
Musca, alleged free nuclear formation,
202
Muscidae, connected with Termito-
xeniidae, 383
Mustelus, placenta, 456
Mutation, periods of, 287, 311
theory of, 319 etc., 325,
348, 373
Mycetozoa, giant cells in, 52
Myrmechusa, intermediate form be-
tween Myrmedonia and Lome-
chusa, 337
Myrmecophile. See Ant-inquilines
Myrmedonia, 337, 343, 346
Myrmica, species, 310
host of Atemeles, 330 etc.
aberrans, 331
laevinodis, 334
lobicornis, 406
myrmicoxena, 406
rubida, 310
rubra, 310, 330, 334
ruginodis, 334
rugulosa, 334
scabrinodis, 334
sulcinodis, 334
Myrmicinae, 400 etc., 406, 413 etc.
Myrmoxenus, 387, 401
Myxomycetes, 52
Myzostoma, fertilisation, 126, 157
NATURAL selection, Darwin's, 257
etc., 490
criticism of, 259 etc.,
312, 314 etc., 326,
328, 339, 347, 376
etc., 423 etc., 490
etc.
Nautilus, phylogeny of, 276
Neandertal man, 467-484, 505 etc.
age of, 470, 505
Neo-Darwinism, Weismann's, 263, 490
Neo-Lamarckism, 264, 493
Neo-vitalism, 238, 493
Noctiluca, centrosomes, 134
conjugation, 132
534
INDEX
Nomenclature, binary, 18-20
Non-nucleate organisms, 49, 180
etc.
Notonecta, maturation, 115, 170
Nuclear division, direct, 87
indirect, 87 etc.
See Karyokinesis
filaments, 61, 62, 64
formation, free, 186, 202
framework, 61, 64, 65, 180
regions for formation of
organs, 219
spindle, 65, 93 etc., 122
Nuclein (see Chromatin), 61, 196
Nucleinic acid, composition of, 196
Nucleoli, 54, 61, 64, 90
Nucleus, bearer of heredity, 83, 84.
152 etc., 160, 163 etc.,
167, 177, 191, 212, 236
etc., 247
discovered byLeeuwenhoek,
31
essential part of cell, 48,
180 etc.
importance of, 77 etc., 83
etc., 180
minute structure of, 60 etc.
See also Karyoplasm and
Karyomitom
(ECOLOGY, 4
(Enothera, in a mutation period,
312
Offensive type of inquiline, 315 etc.,
323 etc., 325, 328, 344 etc.,
350 etc., 354 etc. See
Dinarda, and Dorylinae, in-
quilines
development of, among Aleo-
charinae, 354 etc.
Ontogeny, 7, 208 etc., 254, 449
Oocytes, 109, 110
Oogenesis, 109 etc., 114
Oosperms, 133
Ophryotrocha, maturation-divisions,
114
Orang-utang, blood-reaction, 458
etc.
Organs and organellae, 67
Organs, systems of, 27
Organisation, characteristics due to,
294, 328, 329, 370
stages in, 66 etc.
Organism, a cell or aggregation of
cells, 66 etc.
Organisms, without maternal charac-
teristics, 152
fossil, 274. See Palaeonto-
logy
Organisms — continued
origin of, 193 etc., 279 etc.,
288 etc.
Orthogenesis, Eimer's, 263, 328, 348
Orthogonius, blood-forming tissues,
76
Orthoptera, maturation-divisions, 110,
113, 114. See Grasshopper,
Gryllotalpa, Phasrnidae
Oscillaria, apparent absence of nucleus,
182, 183
Ostracoda, parthenogenesis, 135
Ox, number of chromosomes, 93
P^EDOGENESIS, 135
Palseodictyoptera, 276, 298
Palaeontology, 28, 252, 270, 274, 291,
427, 491
and the phylogeny of ant-
and termite-inquilines,
327 etc.
evidence of, as to origin of
man, 464-480, 497 etc.
Palseophytology, 7, 291
Palseozoology, 7, 291
Palingenesis, Haeckel's theory of,
449
Pandorina, propagation, 132, 160
Pangens, 190
Paramaecium, conjugation, 130 etc.
Paranuclein, 61 etc.
Parasitic ants, 406 etc. See also
Anergates, Epipheidole, Epoe-
cus, Symmyrmica, Sympheidole,
Wheeleria
Parotermes, 277
Parthenogenesis, artificial, 139 etc.
bearing on problem of ferti-
lisation, 145, 157, 163
etc.
facultative and obligatory,
135
generative and somatic,
138
in animals, 135 etc., 139 etc.
in plants, 138, 523
Loeb's experiments, 140
etc.
male, 138, 150
maturation process in, 136
natural, 135 etc.
Paussidae, adaptation to position of
inquilines, 365, 374 etc.
causes of evolution, 373
etc.
hypothetical phylogeny, 297,
364-379
in Baltic amber, 276, 365,
369
INDEX
535
Paussidae — continued
monophyletic or polyphy-
Ictic evolution ? 372
systematic groups of, 365
See also Arthropterus, Cera-
pterus, Homopterus, Hylotorus,
Lebioderus, Paussoides, Pausso-
morphus, Paussus, Pentaplatar-
thrus, Platyrhopalus, Pleuropterus,
Protopaussus
Paussiger, 360
Paussoides, 365, 369 etc.
Paussomorphus, 366
Paussus, 364-379
antennae, 365, 367 etc., 375
etc.
egg-tubes of, 365
exudatory organs and tis-
sues, 366, 370, 374
genuine guest-relationship,
365 etc., 374
armatus, 367
cervinus, 363
cucullatus, 365, 366
cultratus, 377
Gurtisi, 377
dama, 363, 366, 367, 378
elaphus, 363
Elisabethae, 377
granulatus, 377
howa, 366, 367, 378
Klugi, 377
spiniceps, 366, 376
Pedigree of man, Haeckel's, 278, 446
etc., 476 etc., 512
etc.
primates, Haeckel's, 476,
512
Pelomyxa, conjugation, 523
Pentaplatarthrus, 366, 371
Peripatus, collective type, 277
maturation-divisions, 114
placenta, 456
Periplaneta, host of Bacillus, 183
Permanence of species, 255 etc., 286
etc., 396 etc.
theory of, 307-429
and its value, 424 etc.
Peronospora, conjugation, 131
Personal selection, Darwin's, 176,
263
Phagocytes, 72 etc.
Phanerogams, absence of centrosomes,
99
number of chromosomes,
93
Phasniidae, accessory chromosome,
110, 170
parthenogenesis, 139
phylogeny, 276
Pheidole, host of Paussus, 377 etc.
host of Sympheidole and
Epipheidole, 407
ceres, 407
latinoda, 377
megacephala var. punctu-
lata, 377
pilifera var. color adensis, 407
plagiaria, 377
Phoridae, connected with Termito-
xeniidae, 383
Phyllopoda, parthenogenesis, 135
Phylogeny, 7, 234, 251 etc., 291 etc.,
446 etc., 451 etc., 476 etc., 496
etc. See also Evolution
Physiology, 3, 6
cellular, 46, 102
Physogastry in termite -inquilines,
38 etc., 76, 380 etc.
Pithecanthropus, 465, 469, 474 etc., 504
Placenta, resemblance between man
and apes, 456
Planorbis series, Hilgendorf's, 275
Planula larva, 233
Plasomes, 190
Plastidules, 190
Plastin, 61 etc.
Platyrhopalus, 366, 371
Pleuropterus, 366, 371, 378
Pliny the Younger, 10, 11
Pluteus larva of sea-urchin, hybrid,
152, 154
produced by partheno-
genesis, 141
produced bv merogony, 1 49
etc.
produced by merotomy, 228,
231
Podophrya, gemmation, 86
Polar bodies in karyokinesis, 90, 119.
See Centrosomes
in the egg-cell, 109, 136
etc.
Polar nucleus, 137
Polar spindle. See Nuclear spindle
Poles, animal and vegetative, of the
egg, 208, 216, 230
Polyembryony, 129, 135
Polyergus, Amazon ant, 387 etc., 398
etc., 411 etc., 416 etc.
bicolor, 398
breviceps, 398
lucidus, 398
mexicanus, 398
rufescens, 387 etc., 398 etc.
Polygnotus, polyembryony, 135
Polymorphism of protoplasm, 62, 63
Polyphyletic evolution. See Evolution
Polyspermy, pathological and physio-
logical, 127 etc.
536
INDEX
Post-reduction division, 111, 113
Preformation, theory of, 21 1-228. See
also Determination
Pre-reduction division, 111
Primates, pedigree of, 475, 51 1
Primitive forms, 280, 282, 288 etc.,
293 etc.
Primordial plasm, 193
Progonotaxis of man, Haeckel's, 448.
502, 512
Propagation, various forms of, 131 etc.,
135 etc., 155 etc., 159
etc. See Amphimixis,
Fertilisation, Germ-
cells, Isogamy, etc.
agamous, 160, 163
by conjugation, 131
by division, 130 etc.
by gemmation, 86
by heterogony, 136
Prospective potency of cells, 159, 226
etc., 230
value of cells, 226 etc., 230,
232
Protobathybius, 181
Protococcus, 195
Protopaussus, 365, 369, 372
Protophasma, 276
Protoplasm, meaning of, 33 etc., 56
movements of, 70, 73
reacting power of, 281
products of, 75 etc.
Protoplasts, 183
Pselaphidae, 361 etc.
Pselaphus, 361
Pseudogynes, 339
Pseudomitotic division, 111, 112
Pseud opodia, 71
Psychidae, parthenogenesis, 135
Psychology, animal, 500
competent to deal with
origin of man, 282, 433
etc.
distinguished from bio-
logy, 3
Pteridophyta, absence of centrosomes,
99
Pygmy theory, Kollmann's, 475
Pygostenini, offensive type of inquiline,
344 etc., 349 etc., 357
Pygostenus, 344, 426
pubescens, 357
termitophilus, 357 etc.
Pi/rrhocoris, number of chromosomes,
175
QUADRILLE of centres, Fol's, 99
Qualitative differences in chromo-
somes, 169
Qualitative reduction of chroma-
tin, 165
Qualities, mixture of. See Amphimixis
Quantitative reduction of chromatin,
165
RACES. See Subspecies
Radiolaria, movements in, 72
Radium and spontaneous generation,
197
Rat, blood-reaction, 458, 459
maturation-divisions, 113
Redifferentiation, 229, 231, 232
Reducing division, 111-119. See
Maturation-divisions
Reduction of chromatin, 109 etc., 156
etc., 164 etc.
in parthenogenesis,
136, 143 etc.
object of, 164 etc.
Regeneration, 213 etc., 524. See also
Transplantation
Regulation, capacity for, 231
organic, 227, 229
Rejuvenescence, Biitschli's theory of,
161, 173
Reorganisation, R. Hertwig's theory
of, 162
Reptiles, superfecundation in, 128
Rhabdonema, movement of nuclei, 78
Rhizocephala, parasitic degeneration,
327
Rhizopoda, movements in, 71
Rhodites, polar bodies in, 137
Rhozites, cultivated by ants, 345
Rhynchites, species of, 310
Rhysopaussidae, 329
Robber-colonies of ants, 395 etc., 404
etc., 414 etc., 423 etc.
developed from adoption
colonies, 396
Rotatoria, parthenogenesis, 135
Rubus, new types of, 313
Rudimentary organs, 445
SALAMANDER, karyokinesis, 89
number of chromo-
somes, 93, 175
ontogeny, 454
Salix, new types of, 313
Salmon, number of chromosomes, 93,
175
Scarabaeidae, 329
Schematised illustrations, 514
Scorpion, placenta, 456
Sea-mew, blood-reaction, 458
Seasonal dimorphism, 314
Sea-urchin. See Echinus
INDEX
537
Sections, cutting and staining, 34,
36, 41
of ant- and termite- in qui-
lines, 44, 385
of Chaetopisthes, 58
of physogastric termite-
inquilines, 76
of Termitoxenia, 42
Selachii, chromosomes in eggs, 116,
168
experiments on eggs, 234
polyspermy in, 128
Selection. See Germinal, Histonal,
Natural selection
Sensitiveness of plants, 7, 281 etc.
Sharks, placenta, 456
Siphonaceae, multinucleate cells, 54
Slave-keeping ants, 386 etc., 394 etc.,
41 1 etc. See Formica-, Polyergus,
Strong ylognaihus, Tomognathus
Slavery among ants, 386-425
evolution of, 411-425, 492
Smilax, 346
Soul, human, 283 etc., 435 etc.
unlike brute soul, 284, 436
Species of animals and plants, 19 etc.,
267 etc., 286 etc., 307
etc.
as morphological and
biological units, 308
good and bad, 309
systematic and natural,
296 etc., 427 etc., 488
Sperm-cells, diminutive size of, 120,
166
maturation-divisions, 110
etc.
in fertilisation, 108, 119 etc.,
121 etc., 127 etc., 134, 142,
146 etc., 150, 153 etc., 157
etc., 185
Spermaster, 122
Spermatocentrosome, or male centro-
some, 122
as organ of cell-division,
126 etc., 134
importance in fertilisation,
142, 146 etc., 153 etc.,
155, 157
Spermatogenesis, 110 etc., 160, 170
Spermatogonia, 170
Spermatozoa, discovery of, 30
flagelliform, 74, 185
See Sperm-cells
Sphaerechinus, 151
egg-cleavage, 234
Spindle fibres. See Nuclear spindle
Spongioplasm. See Cytoplasm
Spontaneous generation, 179 etc., 186,
193 etc.
Spontaneous generation — continued
and chemistry, 195 etc.
and radium, 197
gradually abandoned, 198
etc.
not a postulate of science,
203, 269
Stains for sections, 34, 41
Staphylinidae, myrmecophile, 315 etc.,
330 etc., 340 etc., 349 etc.
termitophile, 76, 349 etc.
See Aleocharinae, Dinardini,
Lomechusini, Pygostenini, Xeno-
cephalini
Stenamma, 392
Stentor, form of nucleus in, 51
merotomical experiments on,
81 etc.
Strongylocentrotus, 154
Strongylognathus, 400 etc., 412, 414,
418 etc.
afer, 404
Ceciliae, 404
Christophi, 401, 404
Huberi, 401 etc., 404
testaceus, 401 etc., 404 etc.,
410, 414
var. Eehbinderi, 402
Styelopsis, maturation-divisions, 115
Suarez, words bearing upon evolution,
274
Subspecies, 309 etc.
of Dinarda, 321
Superfecundation among animals, 127
etc.
Symmyrmica, 407
Sympheidole, 407
Symphilic colouring in Clavigeridae,
360
type of ant-inquilines, 328.
See also Guest-relation-
ship
Synapsis, 115
Syncytia, 53
Syrbula, spermatogenesis, 170
Syromastes, spermatogenesis, 114
Systematics or Systematic classifica-
tion, and biology, 24
development of, 17 etc.
Linnaeus' ' Systema Natu-
rae,' 18 etc.
recent works on, 20 etc.
Systems, equipotential, 227, 244
harmonious equipotential,
227, 232
Tapinoma, 415
Teleostei, chromosomes in eggs of,
116, 168
538
INDEX
Teleostei — continued
experiments with eggs of,
234
Termes, host of Doryloxenus, Dis-
coxenus and Termitodiscus, 352
etc.
Termite-inquilines, 38 etc., 44, 58,
76, 327 etc., 379 etc.
See Chaetopisthes, Dis-
coxenus, Doryloxenus,
Orthogonius, Pygo-
stenus, Termitodiscus,
Termitoxeniidae, Xeno-
gaster
transformation of ant-
inquilines into, 348
etc. %
Termites, palaeontological evolution
of, 276 etc., 298 etc., 329 etc.
Termitodiscus, 352 etc.
Termitomyia, 40, 53, 64, 75, 381 etc.,
384 etc.'
Termitoxenia, adipose tissues, 44, 50
ametabolia, 39, 380, 382
and evolution, 382-386
cells of, 50 etc.
ciliated cells, 75
imaginal development, 39,
380
microscopical study of, 38
etc.
oogenesis, 38 etc., 52, 380
etc.
pericardial cells, 64
protandric hermaphrodit-
ism, 39, 380
single -tubed ovaries, 39
size of egg-cells, 38, 52
stenogastric and physo-
gastric forms, 39, 380,
384
thoracic appendages, 38,
380, 384, 452
Termitoxeniidae. See Termitomyia and
Termitoxenia
phylogeny of, 382 etc.
Tetrads of chromosomes, 113, 114,
172
Tetramorium, 402 etc., 409, 415
Thalassicola, merotomy, 82
Thallophyta, multinucleate cells, 54
Theism, 205 etc., 249, 299 etc., 427 etc.,
437 etc., 481
Theories in natural science, 269, 285
etc.
Theory of types, Cuvier's, 28
Thiasophila, connected with Dinarda,
325
Thomas Aquinas, St., * lacertae et
tortucae,' 14
Thomas Aquinas — continued
on embryonic forms, 440
principles bearing on evolu-
tion, 274
Thomas of Chantimpre, 11
Thoracic appendages in Termito-
xeniidae, 38, 380, 384, 452
Tissues, blood, 38, 76, 381
exudatory, in ant-inquilines,
44. See Exudation
fatty, 44, 76, 338 etc., 362
glandular, 44, 59, 362, 366,
373
study of. See Histology
systems of, 27
Titanophasma, 276
Tmesiphoroides, 363
Tomognathus, 397, 400 etc., 414
etc.
Torpedo, number of chromosomes,
93
Tradescantia, protoplasmic flow, 74
Transformation of ant-inquilines into
termite-inquilines, 348 etc.
Transplantation, experiments in,
524
Triton, cleavage-spheres, 232
Trochophore larvae of Chaetopterus,
141
Trophoplasm, 162. See Deutero-
plasm
Types, Cuvier's theory of, 28
UNITS, physiological, 190
VARIABILITY of species,not unlimited,
. 260, 309
Varieties, 257, 309 .etc.
Vaucheria, multinucleate cells, 54
Vincent of Beauvais, 11
Vitalism, 211, 219, 238 etc., 242
etc.
Vital laws, 208, 211, 239 etc., 241
etc.
principle, 177, 243 etc.
processes, 69
Vivisection of unicellular organisms.
See Merotomy
Volvocineae, 132
Volvox, mode of propagation, 132
etc.
Vorticella, conjugation, 132
WANDERING ants, 340 etc., 348 etc.
inquilines of, 340
etc., 348 etc.
Wasps, parthenogenesis, 135
INDEX
539
Whale, teeth in embryo, 452, 487,
498
W heeleria, 387, 406 etc., 415
Worms, number of chromosomes,
93
XENIA. See Double fertilisation,
129
Xenocephalini, 344 etc.
Xenocephalus, 344
Xenodusa, 330 etc.
Xenogaster, 76
Zea, double fertilisation, 129
Zoology, development of, 17 etc.
divisions of, 6 etc.
incompetent to judge of
origin of man, 432 etc.,
442
Zoosperms, 133, 138
THE END
PRINTED BY
SPOTTISWOODE AND CO. LTD., COLCHESTER
LONDON AND ETON
Wasmann
Modern biology and the .W2g
theory of e volution . ' °P*2
Wasmann ,QH
371
Modern biology and the .W2B
theory of evolution. cop. 2
Live Music
Archive
Librivox
Free Audio
Metropolitan Museum
Cleveland
Museum of Art
Internet
Arcade
Console Living Room
Open Library
American
Libraries
TV News
Understanding
9/11